Micro-oscillation element and method for driving the same

ABSTRACT

A micro-oscillation element includes a movable main section, a first frame and a second frame, and a first connecting section that connects the movable main section and the first frame and defines a first axis of rotation for a first rotational operation of the movable main section with respect to the first frame. The element further includes a second connecting section that connects the first frame and the second frame and defines a second axis of rotation for a second rotational operation of the first frame and the movable main section with respect to the second frame. A first drive mechanism is provided for generating a driving force for the first rotational operation. A second drive mechanism is provided for generating a driving force for the second rotational operation. The first axis of rotation and the second axis of rotation are not orthogonal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a micro-oscillation element, such as amicro-mirror element having a movable section capable of rotationaldisplacement, and also relates to a drive method for such amicro-oscillation element.

2. Description of the Related Art

In recent years, it has been sought to apply the use of elements havingextremely small structures formed by micro-machining technology, invarious technological fields. For example, in the field of opticalcommunications technology, attention has focused on very smallmicro-mirror elements which have a light reflecting function.

In optical communications, an optical signal is transmitted by using anoptical fiber as a medium, and furthermore, in general, a so-calledoptical switching device is used in order to switch the transmissionpath of the optical signal from one fiber to another fiber.Characteristics required in an optical switching device in order toachieve good optical communications include high capacity, high speedand high reliability, in the switching operation, and the like. Fromthis point of view, expectations have been growing with regard tooptical switching devices which incorporate micro-mirror elementsfabricated by micro-machining technology. This is because the use of amicro-mirror element makes it possible to carrying out switchingprocesses on the optical signal itself, without having to convert theoptical signal to an electrical signal, between the optical transmissionpath on the input side of the optical switching device and the opticaltransmission path on the output side thereof, and this means that it issuitable for obtaining the characteristics described above.

A micro-mirror element is provided with a mirror surface for reflectinglight, and it is capable of changing the direction in which the light isreflected by oscillation of the mirror surface. Electrostatic drive-typemicro-mirror elements which use electrostatic force in order to causethe mirror surface to oscillate are used in many devices. Electrostaticdrive-type micro-mirror elements can be divided broadly into two types:micro-mirror elements manufactured by so-called surface micro-machiningtechnology, and micro-mirror elements manufactured by so-called bulkmicro-machining technology.

In the case of surface micro-machining technology, a thin layer ofmaterial corresponding to a respective constituent area is formed on asubstrate and processed into a prescribed pattern, and such patterns arelayered in a sequential fashion, whereby respective areas constitutingan element, such as a support, mirror surface and electrode section, andthe like, are formed, and a sacrificial layer which is subsequentlyremoved is also formed. On the other hand, in the case of bulkmicro-machining technology, a support and mirror section, and the like,are formed in a prescribed shape by etching the actual material of thesubstrate, mirror surfaces and electrodes being formed as thin layersthereon according to requirements. Bulk micro-machining technology isdescribed, for example, in Japanese Patent Laid-Open No. (Hei)10-190007,Japanese Patent Laid-Open No. (Hei)10-270714 and Japanese PatentLaid-Open No. 2000-31502.

One technical feature required in a micro-mirror element is that themirror surface which performs light reflection has a high degree offlatness. However, in the case of surface micro-machining technology,since the mirror surface ultimately formed is thin, the mirror surfaceis liable to curve, and consequently, it is difficult to achieve a highdegree of flatness in a mirror surface having a large surface area. Onthe other hand, in the case of bulk micro-machining technology, a mirrorsection is constituted by cutting into the actual material substrate,which is relatively thick, by means of an etching process, and since amirror surface is provided on this mirror section, it is possible toensure rigidity, even if the mirror surface has a large surface area.Consequently, it is possible to form a mirror surface having asufficiently high degree of optical flatness.

FIG. 43 and FIG. 44 illustrate a conventional electrostatically drivenmicro-mirror element X8 fabricated by means of bulk micro-machiningtechnology. FIG. 43 is an exploded oblique view of a micro-mirrorelement X8, and FIG. 44 is a cross-sectional view along lineXXXXIV-XXXXIV in FIG. 43 of the micro-mirror element X8 in an assembledstate.

The micro-mirror element X8 has a structure in which a mirror substrate80 and a base substrate 86 are layered on each other. The mirrorsubstrate 80 is constituted by a mirror section 81, a frame 82, and apair of torsion bars 83 linking same together. By performing etchingfrom one side only on a prescribed material substrate, such as a siliconsubstrate having, electrical conductivity, it is possible to form theoutline shape of the mirror section 81, frame 82 and torsion bars 83, onthe mirror substrate 80. A mirror surface 84 is provided on the surfaceof the mirror section 81. A pair of electrodes 85 a, 85 b are providedon the rear face of the mirror section 81. The pair of torsion bars 83define an axis A8 for the rotational operation of the mirror section 81,as described hereinafter. An electrode 87 a opposing the electrode 85 aof the mirror section 81, and an electrode 87 b opposing the electrode85 b are provided on the base substrate 86.

In the micro-mirror element X8, when an electric potential is applied tothe frame 82 of the mirror section 80, the electric potential istransmitted to the electrode 85 a and the electrode 85 b, by means ofthe pair of torsion bars 83 and the mirror section 81, which are formedin an integral fashion from the same conductive material as the frame82. Consequently, by applying a prescribed electric potential to theframe 82, it is possible to charge the electrodes 85 a, 85 b,positively, for example. In this state, if the electrode 87 a of thebase substrate 86 is charged with a negative charge, then anelectrostatic attraction is generated between the electrode 85 a and theelectrode 87 a, and hence the mirror section 81 rotates in the directionof the arrow M8, as indicated in FIG. 44, whilst twisting the pair oftorsion bars 83. The mirror section 81 is able to swing until it reachesan angle at which the force of attraction between the electrodesbalances with the sum of the twisting resistances of the respectivetorsion bars 83. Alternatively, if a negative charge is applied to theelectrode 87 b whilst a positive charge is being applied to theelectrodes 85 a, 85 b of the mirror section 81, then an electrostaticattraction is generated between the electrode 85 b and the electrode 87b, and hence the mirror section 81 will rotate in the opposite directionto the arrow M8. By driving the mirror section 81 to swing as describedabove, it is possible to switch the direction of reflection of the lightreflected by the mirror surface 84.

In the micro-mirror element X8, in order to attain a large angle in therotational displacement of the mirror section 81, it is necessary toensure a sufficient gap between the mirror substrate 80 and the basesubstrate 86, in order to avoid mechanical contact between the mirrorsubstrate 80 and base substrate 86. However, since the electrostaticforce generated between the electrodes 85 a and 87 a, or between theelectrodes 85 b and 87 b, tends to decline as the distance between theelectrodes increases, the drive voltage that is to be applied betweenthe respective electrodes must be increased to a corresponding degree,in order that the mirror section 81 can be driven suitably, whilstguaranteeing a sufficient gap between the mirror substrate 80 and thebase substrate 86. In many cases, increasing the drive voltage isundesirable, in terms of the composition of the element, or from theviewpoint of reducing power consumption.

FIG. 45 is a partially abbreviated oblique diagram of a furtherconventional micro-mirror element X9, which is fabricated by means ofbulk micro-machining technology. The micro-mirror element X9 has amirror section 91 provided with a mirror surface 94 on the upper surfacethereof, a frame 92 (partially omitted), and a pair of torsion bars 93for linking same together. Comb tooth-shaped electrodes 91 a, 91 b areformed at the two respective end portions of the mirror section 91. Apair of comb tooth-shaped electrodes 92 a, 92 b are formed in the frame92, extending in an inward direction in positions corresponding to thecomb tooth-shaped electrodes 91 a, 91 b. A pair of torsion bars 93define an axis A9 for the rotational operation of the mirror section 91with respect to the frame 92.

In a micro-mirror element X9 having a composition of this kind, the setof comb tooth-shaped electrodes provided in adjacent positions in orderto generate an electrostatic force, for example, the comb tooth-shapedelectrode 91 a and the comb tooth-shaped electrode 92 a, are oriented ina two-tier fashion as illustrated in FIG. 46A, when no voltage isapplied to same. On the other hand, when a prescribed voltage isapplied, as illustrated in FIG. 46B, the comb tooth-shaped electrode 91a is drawn inside the comb tooth-shaped electrode 92 a, thereby causingthe mirror section 91 to rotate. More specifically, for example, if thecomb tooth-shaped electrode 91 a is charged with a positive charge, andthe comb tooth-shaped electrode 92 a is charged with a negative charge,then the mirror section 91 will rotate about the axis A9, whilsttwisting the pair of torsion bars 93. By driving the mirror section 91to swing in this fashion, it is possible to switch the direction ofreflection of the light reflected by the mirror surface 94 provided onthe mirror section 91. It is known that the drive voltage required inorder to drive a pair of comb tooth-shaped electrodes of this kind tendsto be lower than the drive voltage required to achieve driving of a pairof planar electrodes, as in the micro-mirror element X8 described above.

FIG. 47 shows a method for manufacturing a micro-mirror element X9. InFIG. 47, the process of forming a portion of the mirror section 91 shownin FIG. 45, and the frame 92, torsion bars 93 and a portion of the setof comb tooth-shaped electrodes 91 a, 92 a, is illustrated by thechanges in a particular cross-section. The cross-section represents acontinuous cross-section which is modeled on a plurality ofcross-sections that are contained within the section in which a singlemicro-switching element is formed on a material substrate (wafer) thatis subjected to various processes.

In the method of manufacturing a micro-mirror element X9, firstly, awafer S9 is prepared as illustrated in FIG. 47A. The wafer S9 is aso-called SOI (Silicon on Insulator) wafer, which has a laminatedstructure comprising a silicon layer 901, a silicon layer 902 and aninsulating layer 903 interposed between these layers. Next, by carryingout anisotropic etching via a prescribed mask on the silicon layer 901,as illustrated in FIG. 47B, the constituent parts that are to be formedin the silicon layer 901 (the mirror section 91, a portion of the frame92, the torsion bars 93, and the comb tooth-shaped electrode 91 a) areformed Next, by carrying out anisotropic etching via a prescribed maskon the silicon layer 902, as illustrated in FIG. 47C, the constituentparts that are to be formed in the silicon layer 902 (a portion of theframe 92, and the comb tooth-shaped electrode 92 a) are formed.Subsequently, as illustrated in FIG. 47D, the exposed portion on thesilicon layer 903 is removed by carrying out isotropic etching on theinsulating layer 903. In this way, the mirror section 91, frame 92,torsion bars 93, and the set of comb tooth-shaped electrodes 91 a, 92 a,are formed. The other set of comb tooth-shaped electrodes 91 b, 92 b areformed in a similar manner to the comb tooth-shaped electrodes 91 a, 91b.

In the micro-mirror element X9, since the comb tooth-shaped electrodes91 a, 91 b are displaced in accordance with the rotational operation ofthe mirror section 91, the comb tooth-shaped electrodes 91 a, 91 b musthave sufficient thickness corresponding to the prescribed angle ofinclination of the mirror section 91. Therefore, in order to achieve alarge angle in the rotational displacement of the mirror section 91 ofthe micro-mirror element X9, it is necessary to design the combtooth-shaped electrodes 91 a, 91 b to be long in the direction ofrotational operation, thus ensuring a sufficient length for the strokeof the drive electrodes (the stroke being the range of relative movementof the electrode pair in the direction of the rotational operation whichis tolerable whilst still being able to generate a suitable drivingforce). In order to ensure a long stroke, in the aforementioned methodof manufacture, it is necessary to carry out processing on a materialsubstrate S9 having silicon layers 901, 902 of a thickness whichcorresponds to the required stroke length. However, it tends to bedifficult to form comb tooth-shaped electrodes 91 a, 91 b wherein eachelectrode tooth has a relatively small width, to a high degree ofaccuracy, by carrying out etching processes, or the like, on relativelythick silicon layers 901, 902.

In addition, in the micro-mirror element X9, since the mirror section 91is formed to the same thickness as the comb tooth-shaped electrodes 91a, 91 b, then the formation of comb tooth-shaped electrodes 91 a, 91 bwhich are long in the direction of rotational operation inevitably leadsto the formation of a thick mirror section 91. The thicker the mirrorsection 91, the greater the mass of the mirror section 91 and hence, thegreater the inertia thereof. Consequently, cases have occurred in whichit is not possible to achieve the desired speed in driving therotational operation of the mirror section 91.

In this way, in a conventional micro-mirror element X9, it has beenproblematic to achieve rotational operation of the mirror section 91involving a large amount of rotational displacement, at a high speed ofoperation.

SUMMARY OF THE INVENTION

The present invention has been proposed under the circumstancesdescribed above. It is therefore an object of the present invention toprovide a micro-oscillation element and a method for drivingmicro-oscillation element suitable for achieving rotational operation ofa movable section involving a large rotational displacement, at a highspeed of operation.

A micro-oscillation element is proposed by a first aspect of the presentinvention. This micro-oscillation element comprises: a movable mainsection; a first and second frame; a first connecting section thatconnects the movable main section and the first frame and defines afirst axis of rotation for a first rotational operation of the movablemain section with respect to the first frame; a second connectingsection that connects the first frame and the second frame and defines asecond axus of rotation for a second rotational operation of the firstframe and the movable main section with respect to the second frame; afirst drive mechanism for generating a driving force for the firstrotational operation; and a second drive mechanism for generating adriving force for the second rotational operation. In the presentelement, the first axis of rotation and the second axis of rotation arenot orthogonal. The first drive mechanism is, for example, constitutedby a set of comb tooth-shaped electrodes, in which case one of the combtooth-shaped electrodes is provided in an integral fashion with respectto the movable main section, and the other comb tooth-shaped electrodeis provided in an integral fashion with respect to the first frame.Moreover, the second drive mechanism is, for example, constituted by aset of comb tooth-shaped electrodes, in which case one of the combtooth-shaped electrodes is provided in an integral fashion with respectto the first frame, and the other comb tooth-shaped electrode isprovided in an integral fashion with respect to the second frame.

In the micro-oscillation element having a composition of this kind, thefirst rotational operation and the second rotational operation of themovable main section include common components of displacement. In otherwords, the overall amount of displacement in these common displacementcomponents corresponds to the sum of the amount of displacementoriginating from the first rotational operation and the amount ofdisplacement originating from the second rotational operation.Therefore, in the common displacement components, the respective strokesof the first and second drive mechanisms are applied in a mutuallyoverlapping fashion, and hence a long stroke can be ensured. Forexample, if the first axis of rotation and the second axis of rotationare mutually coinciding, then the displacement component of the firstrotational operation and the displacement component of the secondrotational operation will coincides entirely, and the total amount ofrotational displacement of the movable main section will correspond tothe sum of the amount of displacement of the first rotational operationand the amount of displacement of the second rotational operation, as aresult of which, a stroke that is effectively longer than the respectivestrokes of the first and second drive mechanisms is ensured in therotational displacement of the movable main section. Since aneffectively long stroke is ensured by superimposition of the strokes oftwo types of drive mechanisms, then it is possible to form therespective drive mechanisms that consist of sets of comb tooth-shapedelectrodes, for example, to a relatively thin size (to a relativelyshort length in the direction of rotational operation). Therefore, themovable section (the movable main section and the first frame) whichtends to be formed to a thickness that reflects the thickness of thedrive mechanisms, can be formed to a relatively-thin size. The thinnerthe movable section, the lighter the weight thereof, and hence the moresuitable it is for achieving high speeds of operation. In this way, themicro-oscillation element according to the first aspect of the presentinvention is suitable for achieving high operating speeds for rotationaloperations of the movable main section involving large amounts ofrotational displacement.

In the first aspect of the present invention, preferably, the firstconnecting section has a cavity section that becomes wider asapproaching the movable main section. In addition to this, or instead ofthis, the second connecting section may have a cavity section thatbecomes wider as approaching the first frame. A composition of this kindis suitable for reducing unwanted displacement components in a directionperpendicular to the desired rotational displacement, for example.

A further micro-oscillation element is proposed by a second aspect ofthe present invention. This micro-oscillation element comprises: amovable section; frame; a connecting section that connects the movablesection and the frame and defines an axis of rotation for a rotationaloperation of the movable section with respect to the frame; a firstdrive mechanism for generating a driving force for the rotationaloperation at a point relatively distant from the axis of rotation; and asecond drive mechanism for generating a driving force for the rotationaloperation at a point relatively close to the axis of rotation. The firstdrive mechanism is, for example, constituted by a set of combtooth-shaped electrodes, in which case one of the comb tooth-shapedelectrodes is provided in an integral fashion with respect to themovable section, and the other comb tooth-shaped electrode is providedin an integral fashion with respect to the frame. Furthermore, thesecond drive mechanism is, for example, constituted by a set of combtooth-shaped electrodes, in which case one of the comb tooth-shapedelectrodes is provided in an integral fashion with respect to themovable section, and the other comb tooth-shaped electrode is providedin an integral fashion with respect to the frame.

In a micro-oscillation element having a composition of this kind, thefirst drive mechanism is more suitable than the second drive mechanismfor generating a larger rotational torque to act as a driving force forrotational operation of the movable section, and the second drivemechanism is more suitable than the first drive mechanism for ensuring alonger stroke. In the micro-oscillation element according to the secondaspect of the present invention, it is possible to achieve goodrotational operation of the movable section, by making effective use ofthese respective characteristics of the two types of drive mechanisms.For example, when the amount of displacement of the movable section iswithin a small angular range, then a large rotational torque can begenerated principally by means of the first drive mechanism, whereas ifit is within a larger angular range, then a prescribed rotational torquecan be sustained by means of the second drive mechanism, throughout therelatively longer stroke of the second drive mechanism. In amicro-oscillation element equipped with both a drive mechanism that issuitable for generating a large rotational torque and a drive mechanismthat is suitable for ensuring a large stroke, it is possible to ensurean effectively large stroke even without forming the respective combtooth-shaped electrodes of the respective drive mechanisms to anexcessively thick size. Therefore, the micro-oscillation elementaccording to the second aspect of the present invention is suitable forachieving high operating speeds for rotational operations of the movablesection involving large amounts of rotational displacement.

In the first and second aspects of the present invention, preferably,the first drive mechanism and the second drive mechanism are constitutedsuch that they can be operated under common control. In this case,preferably, the first drive mechanism and the second drive mechanism areconnected electrically in parallel. Preferably, the first drivemechanism and the second drive mechanism are, alternatively, separatedelectrically, being constituted such that they can be operated undermutually independent control.

A further micro-oscillation element is proposed by a third aspect of thepresent invention. This micro-oscillation element comprises: a movablesection; a frame; a connecting section that connects the movable sectionand the frame and defines an axis of rotation for a rotational operationof the movable section with respect to the frame; and a drive mechanismfor generating a driving force for rotational operation over points thatchange in distance from the axis of rotation continuously. The drivemechanism is, for example, constituted by a set of comb tooth-shapedelectrodes, in which case one of the comb tooth-shaped electrodes isprovided in an integral fashion with respect to the movable section, andthe other comb tooth-shaped electrode is provided in an integral fashionwith respect to the frame.

In a micro-oscillation element having a composition of this kind, thefirst and second drive mechanisms of the second aspect of the inventionare comprised within a single drive mechanism. Therefore, according tothe third aspect of the present invention, similar beneficial effects tothose described above with respect to the second aspect of the inventionare achieved. In addition, according to the third aspect of the presentinvention, the rotational torque generated in a single drive mechanismtends to change gradually and continuously throughout the range ofprescribed rotational operation. This characteristic is suitable forachieving good rotational operation of the movable section.

A further micro-oscillation element is proposed by a fourth aspect ofthe present invention. This micro-oscillation element comprises: amovable section, a frame, a connecting section that connects the movablesection and the frame and defines an axis of rotation for the rotationaloperation of the movable section with respect to the frame, and a drivemechanism comprising a first comb tooth-shaped electrode and a secondcomb tooth-shaped electrode for generating a driving force forrotational operation. The first comb tooth-shaped electrode and/or thesecond comb tooth-shaped electrode have electrode teeth comprising afirst conductor section and second conductor section that areelectrically separated and aligned in parallel with the direction ofrotational operation. For example, the first comb tooth-shaped electrodeis provided in an integral fashion with respect to the movable section,and the second comb tooth-shaped electrode is provided in an integralfashion with respect to the frame.

In this element, the first conductor section and second conductorsection of the first comb tooth-shaped electrode and/or the second combtooth-shaped electrode are aligned in parallel with the direction ofrotational operation of the movable section. A composition of this kindis suitable for ensuring a large relatively range of movement, in otherwords a large stroke, for the pair of comb tooth-shaped electrodes.Moreover, the first conductor section and the second conductor sectionincluded in a single comb tooth-shaped electrode are electricallyseparated from each other and hence the voltages applied to same may becontrolled in an independent fashion. The present swinging elementhaving a first and second conductor section of this kind in at least oneof the pair of comb tooth-shaped electrodes is suitable for achievinghigh operating speeds for rotational operation of the movable sectioninvolving large amounts of rotational displacement.

A further micro-oscillation element is proposed by a fifth aspect of thepresent invention. This micro-oscillation element comprises: a movablesection, a frame, a connecting section that connects the movable sectionand the frame and defines an axis of rotation for the rotationaloperation of the movable section with respect to the frame, and a drivemechanism comprising a first comb tooth-shaped electrode and a secondcomb tooth-shaped electrode for generating a driving force forrotational operation. The first comb tooth-shaped electrode haselectrode teeth comprising a first conductor section and secondconductor section that are electrically connected and aligned inparallel with the direction of rotational operation. The second combtooth-shaped electrode has electrode teeth comprising a third conductorsection that opposes the first conductor section and does not oppose thesecond conductor section when the element is not driven. For example,the second comb tooth-shaped electrode is provided in an integralfashion with respect to the movable section, and the first combtooth-shaped electrode is provided in an integral fashion with respectto the frame.

In this element, the first conductor section and the second conductorsection of the first comb tooth-shaped electrode which generate anelectrostatic attraction with respect to the third conductor section inthe second comb tooth-shaped electrode are aligned in parallel with thedirection of rotational operation of the movable section. A compositionof this kind is suitable for ensuring a large relatively range ofmovement, in other words, a large stroke, for the pair of combtooth-shaped electrodes. Moreover, if the second comb tooth-shapedelectrode (third conductor section) is provided in an integral fashionwith respect to the frame, and the first comb tooth-shaped electrode isprovided in an integral fashion with respect to the movable section,then the second comb tooth-shaped electrode (third conductor section)can be formed to a relatively thin size (relatively short dimension inthe direction of rotational operation), and hence the movable section,which tends to be formed to a thickness that reflects the thickness ofthe second comb tooth-shaped electrode (third conductor section) canalso be formed to a relatively thin size. The thinner the movablesection, the lighter the weight thereof, and hence the more suitable itis for achieving high speeds of operation. In this way, the presentmicro-oscillation element having a pair of comb tooth-shaped electrodesof this kind is suitable for achieving high operating speeds forrotational operation of the movable section involving large amounts ofrotational displacement.

In the fifth aspect of the present invention, preferably, the firstconductor section and third conductor section are of different lengthsin the direction of rotational operation.

In the first to fifth aspects of the present invention, preferably, atleast one of the sets of comb tooth-shaped electrodes constituting thecomb tooth-shaped electrodes has a base section, and electrode teethextending from this base section, these electrode teeth having regionswhich increase gradually in width or thickness towards the end of thebase section side. Alternatively, preferably, at least one of the setsof comb tooth-shaped electrodes constituting the comb tooth-shapedelectrodes comprise a base section and electrode teeth extending fromthis base section, the electrode teeth having regions which increasegradually in width as approaching the other comb tooth-shaped electrode.

In the second to fifth aspects of the present invention, preferably, theconnecting section has a cavity section that becomes wider asapproaching the movable section. A composition of this kind is suitablefor reducing unwanted displacement components in a directionperpendicular to the desired rotational displacement, for example.

A method for driving a micro-oscillation element is proposed by a sixthaspect of the present invention. The micro-oscillation element driven bythis method comprises: a movable section, a frame, a connecting sectionthat connects the movable section and the frame and defines an axis ofrotation for the rotational operation of the movable section withrespect to the frame, and a first comb tooth-shaped electrode and asecond comb tooth-shaped electrode for generating a driving force forrotational operation. The first comb tooth-shaped electrode haselectrode teeth comprising a first conductor section and a secondconductor section aligned in parallel with the direction of rotationaloperation. The first comb tooth-shaped electrode of this kind isprovided in an integral fashion with respect to the frame, for example.The second comb tooth-shaped electrode has electrode teeth-comprising athird conductor section that opposes the first conductor section anddoes not oppose the second conductor section when the element is notdriven. The second comb tooth-shaped electrode of this kind is providedin an integral fashion with respect to the movable section, for example.The present method comprises: a first step for causing the movablesection to perform rotational operation in a first direction bygenerating an electrostatic attraction between the second conductorsection and the third conductor section, and a second step for causingthe movable section to perform rotational operation in a seconddirection, opposite to the first direction, by generating anelectrostatic attraction between the first conductor section and thethird conductor section, subsequently to the first step.

In this method, the first conductor section and the second conductorsection of the first comb tooth-shaped electrode which generate anelectrostatic attraction with respect to the third conductor section inthe second comb tooth-shaped electrode are aligned in parallel with thedirection of rotational operation of the movable section. Therefore,this method is suitable for ensuring a large relatively range ofmovement, in other words, a large stroke, for the pair of combtooth-shaped electrodes. Moreover, in the first and second combtooth-shaped electrodes in the present method, as well as generating adriving force for rotational operation in a first direction, a drivingforce is also generated for rotational operation in a second direction,opposite to the first direction. The present method for generating adriving force in two directions by means of a set of comb tooth-shapedelectrodes is suitable for achieving high operating speeds in rotationaloperation in both directions. In this way, the driving method accordingto the sixth aspect of the present invention is suitable for achievinghigh operating speeds for rotational operation involving large amountsof rotational displacement. What is more, according to the presentmethod, it is possible to drive a micro-oscillation element according tothe fourth aspect of the present invention, for example, in a suitablemanner.

In the sixth aspect of the present invention, preferably, themicro-oscillation element being driven further comprises: a third combtooth-shaped electrode and a fourth comb tooth-shaped electrode forgenerating a driving force for rotational operation. The third combtooth-shaped electrode has electrode teeth comprising a fourth conductorsection and a fifth conductor section aligned in parallel with thedirection of rotational operation. The third comb tooth-shaped electrodeof this kind is provided in an integral fashion with respect to theframe, for example. The third comb tooth-shaped electrode and the firstcomb tooth-shaped electrode described previously are disposed in asymmetrical fashion, for example, with respect to the axis of rotationof the movable section. Moreover, the fourth comb tooth-shaped electrodehas electrode teeth comprising a sixth conductor section that opposesthe fourth conductor section and does not oppose the fifth conductorsection when the element is not driven. The fourth comb tooth-shapedelectrode of this kind is provided in an integral fashion with respectto the movable section, for example. The fourth comb tooth-shapedelectrode and the second comb tooth-shaped electrode describedpreviously are disposed in a symmetrical fashion, for example, withrespect to the axis of rotation of the movable section. If themicro-oscillation element has a composition of this kind, thenpreferably, the driving method according to the sixth aspect furthercomprises a third step for causing the movable section to performrotational operation in a second direction by generating anelectrostatic attraction between the fifth conductor section and thesixth conductor section, subsequently to the second step, and a fourthstep for causing the movable section to perform rotational operation ina first direction by generating an electrostatic attraction between thefourth conductor section and the sixth conductor section, subsequentlyto the third step.

In the sixth aspect of the present invention, preferably, in the secondstep, an electrostatic attraction is generated between the fourthconductor section and the sixth conductor section. Preferably, in thefourth step, an electrostatic attraction is generated between the firstconductor section and the third conductor section. Moreover, preferably,the first, second, third and fourth steps are respectively implementedduring time periods corresponding to one quarter of a cycle of therotational operation.

A further micro-oscillation element is proposed by a seventh aspect ofthe present invention. The micro-oscillation element driven by thepresent method comprises: a movable section, a frame, a connectingsection that connects the movable section and the frame and defines anaxis of rotation for the rotational operation of the movable sectionwith respect to the frame, a first comb tooth-shaped electrode and asecond comb tooth-shaped electrode for generating a driving force forrotational operation, and a third comb tooth-shaped electrode and afourth comb tooth-shaped electrode for generating a driving force forrotational operation at a position closer to the axis of rotation thanthe first and second comb tooth-shaped electrodes. The first and thirdcomb tooth-shaped electrodes are provided in an integral fashion withrespect to the frame, for example. The second and fourth combtooth-shaped electrodes are provided in an integral fashion with respectto the movable section, for example. The present method comprises: afirst step for causing the movable section to perform rotationaloperation in a first direction by generating an electrostatic attractionbetween the first comb tooth-shaped electrode and the second combtooth-shaped electrode, as well as generating an electrostaticattraction between the third comb tooth-shaped electrode and the fourthcomb tooth-shaped electrode, and a second step for causing the movablesection to perform rotational operation in the first direction bygenerating an electrostatic attraction between the third combtooth-shaped electrode and the fourth comb tooth-shaped electrode,subsequently to the first step.

According to the present method, it is possible to drive themicro-oscillation element according to the second aspect of the presentinvention, in a suitable manner, and hence high operating speeds can beachieved in rotational operation involving large amounts of rotationaldisplacement.

Preferably, the driving method according to the seventh aspect of thepresent invention further comprises a third step for causing the movablesection to rotate in a second direction, opposite to the firstdirection, by generating an electrostatic attraction between the firstconductor section and the second conductor section, subsequently to thesecond step. Preferably, the first step and the third step are bothimplemented during a time period corresponding to one quarter of a cycleof the rotational operation.

Preferably, in the seventh aspect of the present invention, themicro-oscillation element further comprises a fifth comb tooth-shapedelectrode and a sixth comb tooth-shaped electrode for generating adriving force for rotational operation, and a seventh comb tooth-shapedelectrode and eighth comb tooth-shaped electrode for generating adriving force for rotational operation at a position closer to the axisof rotation than the fifth and sixth comb tooth-shaped electrodes. Thefifth and seventh comb tooth-shaped electrodes are provided in anintegral fashion with respect to the frame, for example. The sixth andeighth comb tooth-shaped electrodes are provided in an integral fashionwith respect to the movable section, for example. Moreover, the fifthcomb tooth-shaped electrode and the first comb tooth-shaped electrodedescribed previously, the sixth comb tooth-shaped electrode and thesecond comb tooth-shaped electrode described previously, the seventhcomb tooth-shaped electrode and the third comb tooth-shaped electrodedescribed previously, and the eighth comb tooth-shaped electrode and thefourth comb tooth-shaped electrode described previously are respectivelydisposed in a symmetrical fashion, for example, with respect to the axisof rotation of the movable section. If the micro-oscillation element hasa composition of this kind, then preferably, the driving methodaccording to the seventh aspect of the present invention furthercomprises: a fourth step for causing the movable section to performrotational operation in a second direction by generating anelectrostatic attraction between the fifth comb tooth-shaped electrodeand the sixth comb tooth-shaped electrode, as well as generating anelectrostatic attraction between the seventh comb tooth-shaped electrodeand the eighth comb tooth-shaped electrode, subsequently to the thirdstep, and a fifth step for causing the movable section to performrotational operation in a second direction by generating anelectrostatic attraction, following the fourth step, between the seventhcomb tooth-shaped electrode and the eighth comb tooth-shaped electrode.

Preferably, the driving method according to the seventh aspect of thepresent invention further comprises a sixth step for causing the movablesection to rotate in the first direction by generating an electrostaticattraction between the fifth comb tooth-shaped electrode and the sixthcomb tooth-shaped electrode, subsequently to the fifth step. Preferably,the fifth step and the sixth step are both implemented during a timeperiod corresponding to one quarter of a cycle of the rotationaloperation.

A further method for driving a micro-oscillation element is proposed byan eighth aspect of the present invention. The micro-oscillation elementdriven by the present method comprises: a movable section, a frame, aconnecting section that connects the movable section and the frame anddefines an axis of rotation for the rotational operation of the movablesection with respect to the frame, a first comb tooth-shaped electrodeand a second comb tooth-shaped electrode for generating a driving forcefor rotational operation, and a third comb tooth-shaped electrode and afourth comb tooth-shaped electrode for generating a driving force forrotational operation at a position closer to the axis of rotation thanthe first and second comb tooth-shaped electrodes. The first combtooth-shaped electrode has electrode teeth comprising a first conductorsection and a second conductor section aligned in parallel with thedirection of rotational operation. The second comb tooth-shapedelectrode has electrode teeth comprising a third conductor section thatopposes the first conductor section and does not oppose the secondconductor section when the element is not driven. The third combtooth-shaped electrode has electrode teeth comprising a fourth conductorsection and a fifth conductor section aligned in parallel with thedirection of rotational operation. The fourth comb tooth-shapedelectrode has electrode teeth comprising a sixth conductor section thatopposes the fourth conductor section and does not oppose the fifthconductor section when the element is not driven. The first and thirdcomb tooth-shaped electrodes are provided in an integral fashion withrespect to the frame, for example, and the second and fourth combtooth-shaped electrodes are provided in an integral fashion with respectto the movable section, for example. The present method comprises: afirst step for causing the movable section to perform rotationaloperation in a first direction by generating an electrostatic attractionbetween the second conductor section and the third conductor section, aswell as generating an electrostatic attraction between fifth conductorsection and the sixth conductor section, and a second step for causingthe movable section to perform rotational operation in the firstdirection by generating an electrostatic attraction between the fifthconductor section and the sixth conductor section.

A composition of this kind also effectively combines the compositionaccording to the sixth and seventh aspects of the invention describedpreviously. Therefore, according to the eighth aspect of the presentinvention, when driving a micro-oscillation element according to thesecond aspect of the present invention, it is possible to achieve highoperational speeds for rotational operation of the movable sectioninvolving large amounts of rotational displacement.

The driving method according to the eighth aspect of the presentinvention further comprises: a third step for causing the movablesection to perform rotational operation in a second direction, oppositeto the first direction, by generating an electrostatic attractionbetween the first conductor section and the third conductor section,between the second conductor section and the third conductor section,and between the fourth conductor section and the sixth conductorsection, subsequently to the second step, and a fourth step for causingthe movable section to perform rotational operation in the seconddirection by generating an electrostatic attraction, following the thirdstep, between the first conductor section and the third conductorsection, and between the fourth conductor section and the sixthconductor section.

Preferably, in the eighth aspect of the present invention, themicro-oscillation element comprises a fifth comb tooth-shaped electrodeand a sixth comb tooth-shaped electrode for generating a driving forcefor rotational operation, and a seventh comb tooth-shaped electrode andeighth comb tooth-shaped electrode for generating a driving force forrotational operation at a position closer to the axis of rotation thanthe fifth and sixth comb tooth-shaped electrodes. The fifth combtooth-shaped electrode has electrode teeth comprising a seventhconductor section and an eighth conductor section aligned in parallelwith the direction of rotational operation. The sixth comb tooth-shapedelectrode has electrode teeth comprising a ninth conductor section thatopposes the seventh conductor section and does not oppose the eighthconductor section when the element is not driven. The seventh combtooth-shaped electrode has electrode teeth comprising a tenth conductorsection and an eleventh conductor section aligned in parallel with thedirection of rotational operation. The eighth comb tooth-shapedelectrode has electrode teeth comprising a twelfth conductor sectionthat opposes the tenth conductor section and does not oppose theeleventh conductor section when the element is not driven. The fifth andseventh comb tooth-shaped electrodes are provided in an integral fashionwith respect to the frame, for example, and the sixth and eighth combtooth-shaped electrodes are provided in an integral fashion with respectto the movable section, for example. Moreover, the fifth combtooth-shaped electrode and the first comb tooth-shaped electrodedescribed previously, the sixth comb tooth-shaped electrode and thesecond comb tooth-shaped electrode described previously, the seventhcomb tooth-shaped electrode and the third comb tooth-shaped electrodedescribed previously, and the eighth comb tooth-shaped electrode and thefourth comb tooth-shaped electrode described previously are respectivelydisposed in a symmetrical fashion, for example, with respect to the axisof rotation of the movable section. If the micro-oscillation element hasa composition of this kind, then the driving method according to theeighth aspect of the present invention comprises: a fifth step forcausing the movable section to perform rotational operation in a seconddirection by generating an electrostatic attraction between the eighthconductor section and the ninth conductor section, as well as generatingan electrostatic attraction between the eleventh conductor section andthe twelfth conductor section, subsequently to the fourth step; a sixthstep for causing the movable section to perform rotational operation ina second direction by generating an electrostatic attraction, followingthe fifth step, between the eleventh conductor section and the twelfthconductor section; a seventh step for causing the movable section toperform rotational operation in a first direction by generating anelectrostatic attraction between the seventh conductor section and theninth conductor section, between the eighth conductor section and theninth conductor section, and between the tenth conductor section and theeleventh conductor section, subsequently to the sixth step; and aneighth step for causing the movable section to perform rotationaloperation in the first direction by generating an electrostaticattraction, following the seventh step, between the seventh conductorsection and the ninth conductor section, and between the tenth conductorsection and the twelfth conductor section.

In the eighth aspect of the present invention, preferably, in the thirdstep and the fourth step, an electrostatic attraction is generatedbetween the seventh conductor section and the ninth conductor section,and between the tenth conductor section and the twelfth conductorsection. In the eighth aspect of the present invention, preferably, inthe seventh step and the eighth step, an electrostatic attraction isgenerated between the first conductor section and the third conductorsection, and between the fourth conductor section and the sixthconductor section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a micro-mirror element according to a firstembodiment of the present invention;

FIGS. 2A-2C are cross-sectional views along line II-II in FIG. 1;

FIGS. 3A-3B are cross-sectional views along line III-III in FIG. 1;

FIGS. 4A-4B are cross-sectional views along line IV-IV in FIG. 1;

FIGS. 5A-5C are cross-sectional views along line V-V in FIG. 1;

FIGS. 6A-6B are cross-sectional views along line VI-VI in FIG. 1;

FIGS. 7A-7B are cross-sectional view along line VII-VII in FIG. 1;

FIGS. 8A-8C show one example of a drive mode of the micro-mirror elementin FIG. 1;

FIG. 9 is a plan view of a micro-mirror element according to a secondembodiment of the present invention;

FIGS. 10A-10C are cross-sectional views along line X-X in FIG. 9;

FIGS. 11A-11B are cross-sectional views along line XI-XI in FIG. 9;

FIGS. 12A-11B are cross-sectional views along line XII-XII in FIG. 9;

FIGS. 13A-13C are cross-sectional views along line XIII-XIII in FIG. 9;

FIGS. 14A-14B are cross-sectional views along line XIV-XIV in FIG. 9;

FIGS. 15A-15B are cross-sectional views along line XV-XV in FIG. 9;

FIGS. 16A-16D show one example of a drive mode of the micro-mirrorelement in FIG. 9;

FIG. 17 is a plan view of a micro-mirror element according to a thirdembodiment of the present invention;

FIG. 18 is a cross-sectional view along line XVIII-XVIII in FIG. 17;

FIGS. 19A-19B are cross-sectional views along line XVIII-XVIII in FIG.17 when the micro-mirror element is being driven;

FIGS. 20A-20B are cross-sectional view along line XVIII-XVIII in FIG. 17when the micro-mirror element is being driven;

FIGS. 21A-21C are cross-sectional views along line XXI-XXI in FIG. 17;

FIGS. 22A-22C are cross-sectional view along line XXII-XXII in FIG. 17;

FIGS. 23A-23C are cross-sectional views along line XXIII XXIII in FIG.17;

FIGS. 24A-24C are cross-sectional views along line XXIV-XXIV in FIG. 17;

FIGS. 25A-25E show one example of a drive mode of the micro-mirrorelement in FIG. 17;

FIGS. 26A-26E show a further example of a drive mode of the micro-mirrorelement in FIG. 17;

FIG. 27 is a plan view of a micro-mirror element according to a fourthembodiment of the present invention;

FIG. 28 is a cross-sectional view along line XXVIII-XXVIII in FIG. 27;

FIGS. 29A-29B are cross-sectional views along line XXVIII-XXVIII in FIG.27 when the micro-mirror element is being driven;

FIGS. 30A-30B are cross-sectional views along line XXVIII-XXVIII in FIG.27 when the micro-mirror element is being driven;

FIGS. 31A-31C are cross-sectional views along line XXXI-XXXI in FIG. 27;

FIGS. 32A-32C are cross-sectional views along line XXXII-XXXII in FIG.27;

FIGS. 33A-33C are cross-sectional views along line XXXIII-XXXIII in FIG.27;

FIGS. 34A-34C are cross-sectional views along line XXXIV-XXXIV in FIG.27;

FIGS. 35A-35F show one example of a drive mode of the micro-mirrorelement in FIG. 27;

FIG. 36 is a plan view of a micro-mirror element according to a fifthembodiment of the present invention;

FIGS. 37A-37B are cross-sectional views along line XXXVII-XXXVII in FIG.36;

FIGS. 38A-38B are cross-sectional views along line XXXVIII-XXXVIII inFIG. 36;

FIGS. 39A-39B are cross-sectional views along line XXXIX-XXXIX in FIG.36;

FIGS. 40A-40B are cross-sectional view along line XXXX-XXXX in FIG. 36;

FIGS. 41A-41D show a modification of the comb tooth-shaped electrodes;

FIGS. 42A-42B show a further modification of the comb tooth-shapedelectrodes;

FIG. 43 is an exploded oblique view of a conventional micro-mirrorelement;

FIG. 44 is a cross-sectional view along line XXXXIV-XXXXIV of themicro-mirror element in FIG. 43, in an assembled state;

FIG. 45 is partially abbreviated oblique view of a further conventionalmicro-mirror element;

FIGS. 46A-46B show the orientation of a set of comb tooth-shapedelectrodes; and

FIGS. 47A-47D show a portion of the processes of a method formanufacturing the micro-mirror element shown in FIG. 45.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1-FIG. 7 shows a micro-mirror element X1 according to a firstembodiment of the present invention. FIG. 1 is a plan view of themicro-mirror element X1, and FIG. 2 are cross-sectional view along lineII-II in FIG. 1. Furthermore, FIG. 3 to FIG. 7 are cross-sectional viewsalong line III-III, line IV-IV, line V-V, line VI-VI and line VII-VII inFIG. 1, respectively.

The micro-mirror element X1 comprises a mirror section 110, an innerframe 120, an outer frame 130, a pair of connecting sections 140, a pairof connecting sections 150, and respective pairs of drive mechanisms160, 170, 180, 190. Furthermore, the micro-mirror element X1 ismanufactured by carrying out processing on a material substrate, whichis a so-called SOI (silicon on insulator) substrate, by means of bulkmicro-machining technology, such as MEMS technology. The materialsubstrate has a laminated structure consisting, for example, of firstand second silicon layers, and an insulating layer interposed betweenthese silicon layers, a prescribed type of conductivity being impartedto the respective silicon layers, by doping with an impurity. For thepurpose of clarifying the diagrams, in FIG. 1, the regions originatingin the first silicon layer which project beyond the insulating layer inthe direction of the reader are marked by diagonal hatching (with theexception of the mirror surface 111 described hereinafter).

The mirror section 110 is a region formed principally in the firstsilicon layer, and it has a mirror surface 111 having a light reflectingfunction, on the front surface thereof. The mirror surface 111 has alaminated structure consisting of a Cr layer formed on the first siliconlayer, and an Ar layer formed on the Cr layer. The mirror surface 111 ofthis kind forms the principal movable section of the present invention.

The inner frame 120 is a region formed principally in the first siliconlayer, in such a state that it surrounds the mirror section 110. Theinner frame 120 of this kind and the aforementioned mirror section 110constitute a movable section according to the present invention. Theouter frame 130 is a region formed principally in the first siliconlayer, in such a state that it surrounds the inner frame 120.

The pair of connecting sections 140 are regions formed in the firstsilicon layer, and consist respectively of two torsion bars 141. Thetorsion bars 141 are connected to the mirror section 110 and the innerframe 120, thus linking same together. The interval between the twotorsion bars 141 in each respective connecting section 140 graduallyincreases from the inner frame 120 side towards the mirror section 110side. The pair of connecting sections 140 of this kind define an axis A1for the rotational operation of the mirror section 110 with respect tothe inner frame 120. Preferably, the connecting sections 140 are eachconstituted by two torsion bars 141, the interval between whichgradually increases from the inner frame 120 side towards the mirrorsection 110 side, and they prevent unwanted displacement in therotational operation of the mirror section 110. Furthermore, it is alsopossible to constitute the connecting sections 140 such that twodifferent electric potentials can be applied from the inner frame 120 tothe mirror section 110, via the two torsion bars 141.

The pair of connecting sections 150 are regions formed in the firstsilicon layer, and consist respectively of two torsion bars 151. Thetorsion bars 151 are connected to the inner frame 120 and the outerframe 130, thus linking same together. The interval between the twotorsion bars 150 of the respective connecting sections 151 graduallyincreases from the outer frame 130 side towards the inner frame 120side. The axis of rotation of the rotational operation of the innerframe 120 and the mirror section 110 accompanying same, with respect tothe outer frame 130, as defined by the pair of connecting sections 150of this kind, coincides with the rotational axis A1. In other words, thepair of connecting sections 140 and the pair of connecting sections 150are disposed such that the axiss of rotation defined respectively bysame are mutually coinciding. Preferably, the connecting sections 150which are respectively constituted by two torsion bars 151, the intervalbetween which gradually increases from the outer frame 130 side towardsthe inner frame 120 side, prevent unwanted displacement in therotational operation of the inner frame 120 and the mirror section 110.Furthermore, it is also possible to constitute the connecting sections150 such that two different electric potentials can be applied from theouter frame 130 to the inner frame 120, via the two torsion bars 151.

Two drive mechanisms 160 are disposed in a symmetrical fashion, withrespect to the mirror section 110, each comprising a comb tooth-shapedelectrode 161 and comb tooth-shaped electrode 165. The comb tooth-shapedelectrode 161 is a region originating principally in the first siliconlayer, and it has a base section 162 which is fixed to the mirrorsection 110, and a plurality of electrode teeth 163 which project fromthis base section 162. The comb tooth-shaped electrode 165 is a regionoriginating principally in the second silicon layer, and it has a basesection 166 which is fixed to the inner frame 120 and projects in aninward direction, and a plurality of electrode teeth 167 which projectfrom this base section 166. When the element is not driven in rotation,the comb tooth-shaped electrodes 161, 165 are positioned at mutuallydifferent heights, as illustrated by FIG. 2A and FIG. 3A. Moreover, thecomb tooth-shaped electrodes 161, 165 are disposed in a state wherebytheir respective electrode teeth 163, 167 lie in mutually displacedpositions, such that they do not make contact with each other when theelement is driven in rotation.

Two drive mechanisms 170 are disposed in a symmetrical fashion, withrespect to the mirror section 110, each comprising a comb tooth-shapedelectrode 171 and comb tooth-shaped electrode 175. The comb tooth-shapedelectrode 171 is a region originating principally in the first siliconlayer, and it has a base section 172 which is fixed to the mirrorsection 110, and a plurality of electrode teeth 172 which project fromthis base section 173. The comb tooth-shaped electrode 175 is a regionoriginating principally in the second silicon layer, and it has a basesection 176 which is fixed to the inner frame 120 and projects in aninward direction, and a plurality of electrode teeth 176 which projectfrom this base section 177. When the element is not driven in rotation,the comb tooth-shaped electrodes 171, 175 are positioned at mutuallydifferent heights, as illustrated by FIG. 2A and FIG. 4A. Moreover, thecomb tooth-shaped electrodes 171, 175 are disposed in a state wherebytheir respective electrode teeth 173, 177 lie in mutually displacedpositions, such that they do not make contact with each other when theelement is driven in rotation.

Two drive mechanisms 180 are disposed in a symmetrical fashion, withrespect to the mirror section 110 and inner frame 120, each comprising acomb tooth-shaped electrode 181 and a comb tooth-shaped electrode 185.The comb tooth-shaped electrode 181 is a region originating principallyin the first silicon layer, and it has a base section 182 which is fixedto the inner frame 120 and projects in an outward direction, and aplurality of electrode teeth 182 which project from this base section183. The comb tooth-shaped electrode 185 is a region originatingprincipally in the second silicon layer, and it has a base section 186which is fixed to the outer frame 130 and projects in an inwarddirection, and a plurality of electrode teeth 186 which project fromthis base section 187. When the element is not driven in rotation, thecomb tooth-shaped electrodes 181, 185 are positioned at mutuallydifferent heights, as illustrated by FIG. 5A and FIG. 6A. Moreover, thecomb tooth-shaped electrodes 181, 185 are disposed in a state wherebytheir respective electrode teeth 183, 187 lie in mutually displacedpositions, such that they do not make contact with each other when theelement is driven in rotation.

Two drive mechanisms 190 are disposed in a symmetrical fashion, withrespect to the mirror section 110 and inner frame 120, each comprising acomb tooth-shaped electrode 191 and a comb tooth-shaped electrode 195.The comb tooth-shaped electrode 191 is a region originating principallyin the first silicon layer, and it has a base section 192 which is fixedto the inner frame 120 and projects in an outward direction, and aplurality of electrode teeth 192 which project from this base section193. The comb tooth-shaped electrode 195 is a region originatingprincipally in the second silicon layer, and it has a base section 196which is fixed to the outer frame 130 and projects in an inwarddirection, and a plurality of electrode teeth 196 which project fromthis base section 197. When the element is not driven in rotation, thecomb tooth-shaped electrodes 191, 195 are positioned at mutuallydifferent heights, as illustrated by FIG. 5A and FIG. 7A. Moreover, thecomb tooth-shaped electrodes 191, 195 are disposed in a state wherebytheir respective electrode teeth 193, 197 lie in mutually displacedpositions, such that they do not make contact with each other when theelement is driven in rotation.

As described above, the micro-mirror element X1 is manufactured bycarrying out processes on a material substrate having a multiple-layerstructure, by means of bulk micro-machining technology, such as MEMStechnology. Moreover, as described above, in the present embodiment, thematerial substrate has a laminated structure consisting of a first andsecond silicon layer, and an insulating layer interposed between same.

In the manufacture of the micro-mirror element X1, more specifically,respective silicon layers are processed by carrying out etching on amaterial substrate, at prescribed timings, using an etching maskcovering the region corresponding to the mirror section 110, an etchingmask covering the region corresponding to the inner frame 120, anetching mask covering the region corresponding to the outer frame 130,an etching mask covering the region corresponding to the pair ofconnecting sections 140, an etching mask covering the regioncorresponding to the pair of connecting sections 150, an etching maskscovering the regions corresponding to the respective drive mechanisms160, 170, 180, 190, as appropriate. For the etching technique, it ispossible to adopt a dry etching method, such as Deep Reactive IonEtching (RIE), or a wet etching method using KOH, or the like. Theunwanted regions of the insulating layer are removed as appropriate byetching. In this way, the respective regions of the micro-mirror elementX1 are formed on a material substrate having a first and second siliconlayer and an insulating layer. In the present invention, whenmanufacturing the micro-mirror element X1, it is also possible to adopta material substrate having a different laminated structure.

In the micro-mirror element X1, by applying prescribed electricpotentials, as and when necessary, to the respective comb tooth-shapedelectrodes 161, 165, 171, 175, 181, 185, 191, 195, it is possible tocause the mirror section 110 to rotate about the axis of rotation A1.

By applying a prescribed electric potential to the comb tooth-shapedelectrodes 181, 185 of the drive mechanisms 180, a prescribedelectrostatic attraction is generated between the comb tooth-shapedelectrodes 181, 185, whereby the comb tooth-shaped electrode 181 isdrawn inside the comb tooth-shaped electrode 185, such that therespective electrodes assume the orientation illustrated in FIG. 5B andFIG. 6B, for example. By this means, the inner frame 120 and the mirrorsection 110 accompanying same perform rotational operation about theaxis of rotation A1, with respect to the outer frame 130. The amount ofrotational displacement performed in this rotational operation can begoverned by adjusting the applied electric potential.

In a state where the comb tooth-shaped electrodes 181, 185 have assumedthe orientation shown in FIG. 5B and FIG. 6B, if a prescribedelectrostatic attraction is generated between the comb tooth-shapedelectrodes 161, 165 by applying a prescribed electric potential to thecomb tooth-shaped electrodes 161, 165 of the drive mechanisms 160, theneither comb tooth-shaped electrode 161 will be drawn inside the combtooth-shaped electrode 165, and the two electrodes will assume theorientation illustrated in FIG. 2B and FIG. 3B, for example. By thismeans, the mirror section 110 performs rotational operation about theaxis of rotation A1, with respect to the inner frame 120. The amount ofrotational displacement performed in this rotational operation can begoverned by adjusting the applied electric potential.

The overall amount of displacement of the mirror section 110 correspondsto the total of the respective displacements caused by the two types ofrotational movement described above. Rotational operation of the mirrorsection 110 in the opposite direction about the axis of rotation A1 canbe achieved by generating a prescribed electrostatic attraction in thedrive mechanisms 190, similarly to the operation described above withrespect to the drive mechanisms 180, whilst also generating a prescribedelectrostatic attraction in the drive mechanisms 170, similarly to theoperation described above with respect to the drive mechanisms 160, asillustrated in FIG. 2C, FIG. 4B, FIG. 5C and FIG. 7B, for example. Bydriving the mirror section 110 to swing in the above fashion, it ispossible to switch the direction of reflection of the light reflected bythe mirror surface 111 provided on the mirror section 110.

FIG. 8 shows one example of a drive configuration for the micro-mirrorelement X1. FIG. 8A shows the change over time of the voltage applied tothe comb tooth-shaped electrodes 165 of the drive mechanisms 160 and thecomb tooth-shaped electrodes 185 of the drive mechanisms 180. FIG. 8Bshows the change over time of the voltage applied to the combtooth-shaped electrodes 175 of the drive mechanisms 170 and the combtooth-shaped electrodes 195 of the drive mechanisms 190. In the graph inFIG. 8A and the graph in FIG. 8B, the time (t) is represented on thehorizontal axis, and the applied voltage (v) is represented on thevertical axis. In the present drive mode, the comb tooth-shapedelectrodes 161, 171, 181, 191 are connected to ground. Furthermore, FIG.8C shows the change over time of the angle of rotation of the mirrorsection 110 in the present drive mode. In the graph in FIG. 8C, time (t)is represented on the horizontal axis, and the angle of rotation (θ) isrepresented on the vertical axis.

In the present drive mode, firstly, a prescribed voltage V₁ is appliedbetween time T₀ and time T₁, as shown in FIG. 8A, to the respective combtooth-shaped electrodes 165, 185 of the micro-mirror element X1 in aninitial state (where the angle of rotation of the mirror section 110 is0°) at time T₀, such that the rotational displacement of the mirrorsection 110 reaches a maximum angle of rotation θ₁ at time T₁. Betweentime T₀ and T₁, an electrostatic attraction is generated between thecomb tooth-shaped electrodes 161, 165 and the comb tooth-shapedelectrodes 181, 185, and the angle of rotation of the mirror section 110increases continuously in a first direction. At time T₁, the drivemechanisms 160 assume the orientation illustrated in FIG. 2B and FIG.3B, for example, and the drive mechanisms 180 assume the orientationillustrated in FIG. 5B and FIG. 6B, for example, whilst the angle ofrotation reaches θ₁ as illustrated in FIG. 8C. In this case, aprescribed twisting reaction is generated in the connecting sections140, 150.

Thereupon, at time T₁, the applied voltage to the respective combtooth-shaped electrodes 165, 185 is set substantially to 0V.Subsequently, between time T₁ and T₂, the twisting reaction of theconnecting sections 140, 150 acts as a restoring force, and the angle ofrotation decreases continuously. At time T₂, the drive mechanisms 160,170 assume the orientation illustrated in FIG. 2A, FIG. 3A and FIG. 4A,and the drive mechanisms 180, 190 assume the orientation illustrated inFIG. 5A, FIG. 6A and FIG. 7A, whilst the angle of rotation reaches 0° asillustrated in FIG. 8C.

Thereupon, between time T₂ and time T₃, a prescribed voltage V₂ isapplied to the respective comb tooth-shaped electrodes 175, 195, asillustrated in FIG. 8B, such that the rotational displacement of themirror section 110 reaches a maximum angle of rotation θ₂ at time T₃.Between time T₂ and T₃, an electrostatic attraction is generated betweenthe comb tooth-shaped electrodes 171, 175 and the comb tooth-shapedelectrodes 191, 195, and the angle of rotation of the mirror section 110increases continuously in a second direction that is opposite to thefirst direction. At time T₃, the drive mechanisms 170 assume theorientation illustrated in FIG. 2C and FIG. 4B, for example, and thedrive mechanisms 190 assume the orientation illustrated in FIG. 5C andFIG. 7B, for example, whilst the angle of rotation reaches θ₂ asillustrated in FIG. 8C. In this case, a prescribed twisting reaction isgenerated in the connecting sections 140, 150.

Thereupon, at time T₃, the applied voltage to the respective combtooth-shaped electrodes 175, 195 is set substantially to 0V.Subsequently, between time T₃ and T₄, the twisting reaction of theconnecting sections 140, 150 acts as a restoring force, and the angle ofrotation decreases continuously. At time T₄, the drive mechanisms 160,170 assume the orientation illustrated in FIG. 2A, FIG. 3A and FIG. 4A,and the drive mechanisms 180, 190 assume the orientation illustrated inFIG. 5A, FIG. 6A and FIG. 7A, whilst the angle of rotation reaches 0° asillustrated in FIG. 8C. The sequence of operations described above, fromtime T₀ time T₄ are repeated, according to requirements.

In the present drive mode, preferably, the voltage V₁ and the voltage V₂are the same, and the absolute value of the angle of rotation θ₁ is thesame as the absolute value of the angle of rotation θ₂. Moreover, therespective periods between time T₀ and time T₁, between time T₁ and timeT₂, between time T₂ and time T₃, and between time T₃ and time T₄ arepreferably set to the same length, and each constitute respectively onequarter of a cycle of the swinging operation of the mirror section 110.In this way, it is possible to achieve a cyclical rotational operationof the mirror section 110 of the micro-mirror element X1.

In the micro-mirror element X1, the stroke of the drive mechanisms 180and the stroke of the drive mechanisms 160, or the stroke of the drivemechanisms 190 and the stroke of the drive mechanisms 170, are mutuallysuperimposed and thus a long stroke is ensured. Since an effectivelylong stroke is ensured by superimposition of the strokes of two types ofdrive mechanisms, then it is possible to form the respective drivemechanisms formed by sets of comb tooth-shaped electrodes, for example,to a relatively thin size (to a relatively short length in the directionof rotational operation). Therefore, the movable section (mirror section110 and inner frame 120) which tends to be formed to a thickness thatreflects the thickness of the drive mechanisms, can be formed to arelatively thin size. The thinner the movable section, the lighter theweight thereof, and hence the more suitable it is for achieving highspeeds of operation. In this way, the micro-mirror element X1 issuitable for achieving a high speed of operation for rotationaloperations of the mirror section 110 involving large amounts ofrotational displacement.

In the micro-mirror element X1, by disposing the drive-mechanisms 160and the drive mechanisms 180 electrically in parallel, and disposing thedrive mechanisms 170 and the drive mechanisms 190 electrically inparallel, it is possible to simplify the control of the rotational driveoperation. For example, if the respective comb tooth-shaped electrodes161 of the two drive mechanisms 160 and the respective comb tooth-shapedelectrodes 181 of the two drive mechanisms 180 are disposed electricallyin parallel, and if the respective comb tooth-shaped electrodes 165 ofthe two drive mechanisms 160 and the respective comb tooth-shapedelectrodes 185 of the two drive mechanisms 180 are disposed electricallyin parallel, then when driving rotation, the same electrical potentialis applied simultaneously to all of the comb tooth-shaped electrodes161, 181, and the same electrical potential is applied simultaneously toall of the comb tooth-shaped electrodes 165, 185, and hence it ispossible to achieve common control of the drive mechanisms 160, 180.Moreover, if the respective comb tooth-shaped electrodes 170 of the twodrive mechanisms 171 and the respective comb tooth-shaped electrodes 190of the two drive mechanisms 191 are disposed electrically in parallel,and if the respective comb tooth-shaped electrodes 175 of the two drivemechanisms 170 and the respective comb tooth-shaped electrodes 195 ofthe two drive mechanisms 190 are disposed electrically in parallel, thenwhen driving rotation, the same electrical potential is appliedsimultaneously to all of the comb tooth-shaped electrodes 171, 191, andthe same electrical potential is applied simultaneously to all of thecomb tooth-shaped electrodes 175, 195, and hence it is possible toachieve common control of the drive mechanisms 170, 190.

In a design in which the maximum relative angle of rotationaldisplacement of the mirror section 110 with respect to the inner frame120 that can be achieved by means of the drive mechanisms 160, 170, andthe maximum relative angle of rotational displacement of the inner frame120 with respect to the outer frame 130 that can be achieved by means ofthe drive mechanisms 180, 190, are set so as to be equal, if the drivemechanisms 160, 180 are controlled commonly as described above, forexample, and if the drive mechanisms 170, 190 are controlled commonly asdescribed above, for example, then taking the twisting spring constantof the connecting sections 140, 150 to be k₁ and k₂ respectively, andthe rotational torque generated by the drive mechanisms 160, 170 and thedrive mechanisms 180, 190 to be T₁ and T₂, respectively, it is possibleto control the drive mechanisms with the greatest level of efficiencywhen the conditions in equation (1) below are satisfied. On the otherhand, in a design in which the ratio between the maximum relative angleof rotational displacement of the mirror section 110 with respect to theinner frame 120 that can be achieved by means of the drive mechanisms160, 170, and the maximum relative angle of rotational displacement ofthe inner frame 120 with respect to the outer frame 130 that can beachieved by means of the drive mechanisms 180, 190, is set to be 1:a, ifthe drive mechanisms 160, 180 are controlled commonly as describedabove, for example, and if the drive mechanisms 170, 190 are controlledcommonly as described above, for example, then taking the twistingspring constant of the connecting sections 140, 150 to be k₁ and k₂respectively, and the rotational torque generated by the drivemechanisms 160, 170 and the drive-mechanisms 180, 190 to be T₁ and T₂,respectively, it is possible to control the drive mechanisms with thegreatest level of efficiency when the conditions in equation (2) beloware satisfied. Furthermore, if the inertias of the mirror section 110and the inner frame 120 are taken to be I₁ and I₂, respectively, thenpreferably, the values of k₁/I₁ and k₂/(I₁+I₂) should be equal in themicro-mirror element X1.

k ₁ /T ₁ =k ₂ /T ₂  (1)

a(k ₁ /T ₁ =k ₂ /T ₂)  (2)

In the micro-mirror element X1, by disposing the drive mechanisms 160and the drive mechanisms 180 in electrically separate fashion, anddisposing the drive mechanisms 170 and the drive mechanisms 190 inelectrically separate fashion, it is possible to achieve high precisionin the control of the rotational drive operation. If a composition ofthis kind is adopted, then by independently adjusting the driving forceor rotational torque generated by the respective drive mechanisms 160,170, 180, 190, it is possible to control the two types of rotationaloperation about the axis of rotation A1, independently. In this casealso, it is desirable that the conditions stipulated in Equation (1) orEquation (2) are satisfied.

FIG. 9-FIG. 15 show a micro-mirror element X2 according to a secondembodiment of the present invention. FIG. 9 is a plan view of themicro-mirror element X2, and FIG. 10 is a cross-sectional view alongline X-X in FIG. 9. Furthermore, FIG. 11 to FIG. 15 are cross-sectionalviews along line XI-XI, line XII-XII, line XIII-XIII, line XIV-XIV andline XV-XV in FIG. 9, respectively.

The micro-mirror element X2 comprises a mirror section 110, an innerframe 120, an outer frame 130, a pair of connecting sections 140, a pairof connecting sections 150, and respective pairs of drive mechanisms260, 270, 280, 290. The micro-mirror element X2 differs from themicro-mirror element X1 in respect of the fact that it is equipped withdrive mechanisms 260, 270, 280 and 290, instead of the drive mechanisms160, 170, 180 and 190. Moreover, similarly to the micro-mirror elementX1, the micro-mirror element X2 is manufactured by carrying outprocessing on a material substrate, which is an SOI substrate, by meansof a bulk micro-machining technology, such as MEMS technology, or thelike. The material substrate has a laminated structure consisting, forexample, of first and second silicon layers, and an insulating layerinterposed between these silicon layers, a prescribed type ofconductivity being imparted to the respective silicon layers by dopingwith an impurity. For the purpose of clarifying the diagrams, in FIG. 9,the areas originating in the first silicon layer which project in thedirection of the reader beyond the insulating layer are marked bydiagonal hatching (with the exception of the mirror surface 111).

Two drive mechanisms 260 provided in the micro-mirror element X2 aredisposed in a symmetrical fashion, with respect to the mirror section110, each comprising a comb tooth-shaped electrode 261 and combtooth-shaped electrode 265. The comb tooth-shaped electrode 261 is aregion originating principally in the first silicon layer, and it has abase section 262 which is fixed to the mirror section 110, and aplurality of electrode teeth 262 which project from this base section263. The comb tooth-shaped electrode 265 has a laminated structureconsisting of a conductor section 265 a, a conductor section 265 b, andan insulating section 265 c for electrically separating the twoconductor sections, and also has a base section 266 which is fixed tothe inner frame 120 and projects in an inward direction, and a pluralityof electrode teeth 267 which project from this base section 266. Theconductor sections 265 a, 265 b are regions which originate respectivelyin the first and second silicon layer. When the element is not driven inrotation, the comb tooth-shaped electrode 261 and the base section 265 bof the comb tooth-shaped electrode 265 are positioned at mutuallydifferent heights, as illustrated by FIG. 10A and FIG. 11A. Moreover,the comb tooth-shaped electrodes 261, 265 are disposed in a statewhereby their respective electrode teeth 263, 267 lie in mutuallydisplaced positions, such that they do not make contact with each other.

Two drive mechanisms 270 are disposed in a symmetrical fashion, withrespect to the mirror section 110, each comprising a comb tooth-shapedelectrode 271 and comb tooth-shaped electrode 275. The comb tooth-shapedelectrode 271 is a region originating principally in the first siliconlayer, and it has a base section 272 which is fixed to the mirrorsection 110, and a plurality of electrode teeth 272 which project fromthis base section 273. The comb tooth-shaped electrode 275 has alaminated structure consisting of a conductor section 275 a, a conductorsection 275 b, and an insulating section 275 c for electricallyseparating the two conductor sections, and also has a base section 276which is fixed to the inner frame 120 and projects in an inwarddirection, and a plurality of electrode teeth 277 which project fromthis base section 276. The conductor sections 275 a, 275 b are regionswhich originate respectively in the first and second silicon layers.When the element is not driven in rotation, the comb tooth-shapedelectrode 271 and the base section 275 b of the comb tooth-shapedelectrode 275 are positioned at mutually different heights, asillustrated by FIG. 10A and FIG. 12A. Moreover, the comb tooth-shapedelectrodes 271, 275 are disposed in a state whereby their respectiveelectrode teeth 273, 277 lie in mutually displaced positions, such thatthey do not make contact with each other.

Two drive mechanisms 280 are disposed in a symmetrical fashion, withrespect to the mirror section 110 and inner frame 120, each comprising acomb tooth-shaped electrode 281 and a comb tooth-shaped electrode 285.The comb tooth-shaped electrode 281 is a region originating principallyin the first silicon layer, and it has a base section 282 which is fixedto the inner frame 120, and a plurality of electrode teeth 283 whichproject from this base section 282. The comb tooth-shaped electrode 285has a laminated structure consisting of a conductor section 285 a, aconductor section 285 b, and an insulating section 285 c forelectrically separating the two conductor sections, and also has a basesection 286 which is fixed to the outer frame 130 and projects in aninward direction, and a plurality of electrode teeth 287 which projectfrom this base section 286. The conductor sections 285 a, 285 b areregions which originate respectively in the first and second siliconlayers. When the element is not driven in rotation, the combtooth-shaped electrode 281 and the base section 285 b of the combtooth-shaped electrode 285 are positioned at mutually different heights,as illustrated by FIG. 13A and FIG. 14A. Moreover, the comb tooth-shapedelectrodes 281, 285 are disposed in a state whereby their respectiveelectrode teeth 283, 287 lie in mutually displaced positions, such thatthey do not make contact with each other.

Two drive mechanisms 290 are disposed in a symmetrical fashion, withrespect to the mirror section 110 and inner frame 120, each comprising acomb tooth-shaped electrode 291 and a comb tooth-shaped electrode 295.The comb tooth-shaped electrode 291 is a region originating principallyin the first silicon layer, and it has a base section 292 which is fixedto the inner frame 120, and a plurality of electrode teeth 292 whichproject from this base section 293. The comb tooth-shaped electrode 295has a laminated structure consisting of a conductor section 295 a, aconductor section 295 b, and an insulating section 295 c forelectrically separating the two conductor sections, and also has a basesection 296 which is fixed to the outer frame 130 and projects in aninward direction, and a plurality of electrode teeth 297 which projectfrom this base section 296. The conductor sections 295 a, 295 b areregions which originate respectively in the first and second siliconlayers. When the element is not driven in rotation, the combtooth-shaped electrode 291 and the base section 295 b of the combtooth-shaped electrode 295 are positioned at mutually different heights,as illustrated by FIG. 13A and FIG. 15A. Moreover, the comb tooth-shapedelectrodes 291, 295 are disposed in a state whereby their respectiveelectrode teeth 293, 297 lie in mutually displaced positions, such thatthey do not make contact with each other.

In the micro-mirror element X2, by applying prescribed electricpotentials, as and when necessary, to the comb tooth-shaped electrodes261, 271, 281, 291, the conductor sections 265 a, 265 b of the combtooth-shaped electrodes 265, the conductor sections 275 a, 275 b of thecomb tooth-shaped electrodes 275, the conductor sections 285 a, 285 b ofthe comb tooth-shaped electrodes 285, and the conductors sections 295 a,295 b of the comb tooth-shaped electrodes 295, it is possible to causethe mirror section 110 to perform rotational operation about the axis ofrotation A1.

FIG. 16 shows one example of a drive mode for the micro-mirror elementX2. FIG. 16A shows the change over time of the voltage applied to theconductor sections 265 b of the comb tooth-shaped electrodes 265 of thedrive mechanisms 260 and the conductor sections 285 b of the combtooth-shaped electrodes 285 of the drive mechanisms 280. FIG. 16B showsthe change over time of the voltage applied to the conductor sections275 b of the comb tooth-shaped electrodes 275 of the drive mechanisms270 and the conductor sections 295 b of the comb tooth-shaped electrodes295 of the drive mechanisms 290. FIG. 16C shows the change over time ofthe voltage applied to the conductor sections 265 a of the combtooth-shaped electrodes 265 of the drive mechanisms 260, the conductorsection 275 a of the comb tooth-shaped electrodes 275 of the drivemechanisms 270, the conductor sections 285 a of the comb tooth-shapedelectrodes 285 of the drive mechanisms 280, and the conductor sections295 a of the comb tooth-shaped electrodes 295 of the drive mechanisms290. In the respective graphs in FIG. 16A-FIG. 16C, the time (t) isrepresented on the horizontal axis, and the applied voltage (v) isrepresented on the vertical axis. In the present drive mode, the combtooth-shaped electrodes 261, 271, 281, 291 are connected to ground.Furthermore, FIG. 16D shows the change over time of the angle ofrotation of the mirror section 110 in the present drive mode. In thegraph in FIG. 16D, time (t) is represented on the horizontal axis, andthe angle of rotation (θ) is represented on the vertical axis.

In the present drive mode, firstly, a prescribed voltage V₁ is appliedbetween time T₀ and time T₁, as shown in FIG. 16A, to the conductorsections 265 b, 285 b of the respective comb tooth-shaped electrodes265, 285 of the micro-mirror element X2 in an initial state (where theangle of rotation of the mirror section 110 is 0°) at time T₀, such thatthe rotational displacement of the mirror section 110 reaches a maximumangle of rotation θ₁ at time T₁. Between time T₀ and T₁, anelectrostatic attraction is generated between the each comb tooth-shapedelectrode 261 and the conductor section 265 b, and between each combtooth-shaped electrode 281 and the conductor section 285 b, and theangle of rotation of the mirror section 110 increases continuously in afirst direction. At time T₁, the drive mechanisms 260 assume theorientation illustrated in FIG. 10B and FIG. 11B, for example, and thedrive mechanisms 280 assume the orientation illustrated in FIG. 13B andFIG. 14B, for example, whilst the angle of rotation reaches θ₁, asillustrated in FIG. 16D. In this case, a prescribed twisting reaction isgenerated in the connecting sections 140, 150.

Next, between time T₁ and time T₂, the voltage applied to the conductorsections 265 b, 285 b is set substantially to zero, and a prescribedvoltage V₂ is applied to the respective conductor sections 265 a, 275 a,285 a, 295 a, as illustrated in FIG. 16B During this time period, inaddition to the twisting reactions of the connecting sections 140, 150acting as restoring forces, an electrostatic attraction is generatedbetween the comb tooth-shaped electrode 261 and the conductor section265 b, between the comb tooth-shaped electrode 271 and the conductorsection 275 b, between the comb tooth-shaped electrode 281 and theconductor section 285 b, and between the comb tooth-shaped electrode 291and the conductor section 295 b, and hence the angle of rotation of themirror section 110 decreases continuously. At time T₂, the drivemechanisms 260, 270 assume the orientation illustrated in FIG. 10A, FIG.11A and FIG. 12A, and the drive mechanisms 280, 290 assume theorientation illustrated in FIG. 13A, FIG. 14A and FIG. 15A, whilst theangle of rotation reaches 0° as illustrated in FIG. 16D.

Thereupon, between time T₂ and time T₃, a prescribed voltage V₃ isapplied to the respective conductor sections 275 b, 295 b, and thevoltage applied to the respective conductor sections 265 a, 275 a, 285a, 295 a is set substantially to 0V, as illustrated in FIG. 16B, suchthat the rotational displacement of the mirror section 110 reaches amaximum angle of rotation θ₂ at time T₃. Between time T₂ and T₃, anelectrostatic attraction is generated between each comb tooth-shapedelectrode 271 and the conductor section 275 b, and between each combtooth-shaped electrode 291 and the conductor section 295 b, and theangle of rotation of the mirror section 110 increases continuously in asecond direction which is opposite to the first direction. At time T₃,the drive mechanisms 270 assume the orientation illustrated in FIG. 10Cand FIG. 12B, for example, and the drive mechanisms 290 assume theorientation illustrated in FIG. 13C and FIG. 15B, for example, whilstthe angle of rotation reaches θ₂ as illustrated in FIG. 16D. In thiscase, a prescribed twisting reaction is generated in the connectingsections 140, 150.

Next, between time T₃ and time T₄, the voltage applied to the conductorsections 275 b, 295 b is set substantially to zero, and a prescribedvoltage V₄ is applied to the respective conductor sections 265 a, 275 a,285 a, 295 a, as illustrated in FIG. 16C. During this time period, inaddition to the twisting reactions of the connecting sections 140, 150acting as restoring forces, an electrostatic attraction is generatedbetween the comb tooth-shaped electrode 261 and the conductor section265 b, between the comb tooth-shaped electrode 271 and the conductorsection 275 b, between the comb tooth-shaped electrode 281 and theconductor section 285 b, and between the comb tooth-shaped electrode 291and the conductor section 295 b, and hence the angle of rotation of themirror section 110 decreases continuously. At time T₄, the drivemechanisms 260, 270 assume the orientation illustrated in FIG. 10A, FIG.11A and FIG. 12A, and the drive mechanisms 280, 290 assume theorientation illustrated in FIG. 13A, FIG. 14A and FIG. 15A, whilst theangle of rotation reaches 0° as illustrated in FIG. 16D. The sequence ofoperations described above, from time T₀ to time T₄, are repeated,according to requirements.

In the present drive mode, preferably, the voltage V₁ and the voltage V₃are the same, the voltage V₂ and the voltage V₄ are the same, and theabsolute value of the angle of rotation θ₁ is the same as the absolutevalue of the angle of rotation θ₂. Moreover, preferably, the voltages V₂and V₄ are less than the voltages V₁ and V₃. Moreover, preferably, therespective periods between time T₀ and time T₁, between time T₁ and timeT₂, between time T₂ and time T₃, and between time T₃ and time T₄ are setto the same length, and each constitute respectively one quarter of acycle of the rotational operation of the mirror section 110. In thisway, it is possible to achieve a cyclical rotational operation of themirror section 110 of the micro-mirror element X2.

In the micro-mirror element X2, the stroke of the drive mechanisms 280and the stroke of the drive mechanisms 260, or the stroke of the drivemechanisms 290 and the stroke of the drive mechanisms 270, are mutuallysuperimposed and thus a long stroke is ensured. Since an effectivelylong stroke is ensured by superimposition of the strokes of two types ofdrive mechanisms, then it is possible to form the respective drivemechanisms formed by sets of comb tooth-shaped electrodes, for example,to a relatively thin size (to a relatively short length in the directionof rotational operation). Therefore, the movable section (mirror section110 and inner frame 120) which tends to be formed to a thickness thatreflects the thickness of the drive mechanisms, can be formed to arelatively thin size. The thinner the movable section, the lighter theweight thereof, and hence the more suitable it is for achieving highspeeds of operation. In this way, the micro-mirror element X2 issuitable for achieving a high speed of operation for rotationaloperations of the mirror section 110 involving large amounts ofrotational displacement.

In the micro-mirror element X2, by disposing the drive mechanisms 260and the drive mechanisms 280 electrically in parallel, and disposing thedrive mechanisms 270 and the drive mechanisms 290 electrically inparallel, it is possible to simplify the control of the rotational driveoperation. For example, if the respective comb tooth-shaped electrodes261 and the respective comb tooth-shaped electrodes 281 are disposedelectrically in parallel, the conductor sections 265 a of the respectivecomb tooth-shaped electrodes 265 and the conductor sections 285 a of therespective comb tooth-shaped electrodes 285 are disposed electrically inparallel, and the conductor sections 265 b of the respective combtooth-shaped electrodes 265 and the conductor sections 285 b of therespective comb tooth-shaped electrodes 285 are disposed electrically inparallel, then when driving rotation, the same electric potential willbe supplied simultaneously to all of the comb tooth-shaped electrodes261, 281, simultaneously, the same electric potential will be suppliedsimultaneously to all of the conductor sections 265 a, 285 a, and thesame electric potential will be supplied simultaneously to all of theconductor sections 265 b, 285 b, and consequently it is possible toperform common control of the drive mechanisms 260, 280. Moreover, ifthe respective comb tooth-shaped electrodes 271 and the respective combtooth-shaped electrodes 291 are disposed electrically in parallel, theconductor sections 275 a of the respective comb tooth-shaped electrodes275 and the conductor sections 295 a of the respective comb tooth-shapedelectrodes 295 are disposed electrically in parallel, and the conductorsections 275 b of the respective comb tooth-shaped electrodes 275 andthe conductor sections 295 b of the respective comb tooth-shapedelectrodes 295 are disposed electrically in parallel, then when drivingrotation, the same electric potential will be supplied simultaneously toall of the comb tooth-shaped electrodes 271, 291, simultaneously, thesame electric potential will be supplied simultaneously to all of theconductor sections 275 a, 295 a, and the same electric potential will besupplied simultaneously to all of the conductor sections 275 b, 295 b,and consequently it is possible to perform common control of the drivemechanisms 270, 290.

In a design in which the maximum relative angle of rotationaldisplacement of the mirror section 110 with respect to the inner frame120 that can be achieved by means of the drive mechanisms 260, 270, andthe maximum relative angle of rotational displacement of the inner frame120 with respect to the outer frame 130 that can be achieved by means ofthe drive mechanisms 280, 290, are set so as to be equal, if the drivemechanisms 260, 280 are controlled commonly as described above, forexample, and if the drive mechanisms 270, 290 are controlled commonly asdescribed above, for example, then taking the twisting spring constantof the connecting sections 140, 150 to be k₁ and k₂ respectively, andthe rotational torque generated by the drive mechanisms 260, 270 and thedrive mechanisms 280, 290 to be T₁ and T₂, respectively, it is possibleto control the drive mechanisms with the greatest level of efficiencywhen the conditions in equation (1) above are satisfied. On the otherhand, in a design in which the ratio between the maximum relative angleof rotational displacement of the mirror section 110 with respect to theinner frame 120 that can be achieved by means of the drive mechanisms260, 270, and the maximum relative angle of rotational displacement ofthe inner frame 120 with respect to the outer frame 130 that can beachieved by means of the drive mechanisms 280, 290, is set to be 1:a, ifthe drive mechanisms 260, 280 are controlled commonly as describedabove, for example, and if the drive mechanisms 270, 290 are controlledcommonly as described above, for example, then taking the twistingspring constant of the connecting sections 140, 150 to be k₁ and k₂respectively, and the rotational torque generated by the drivemechanisms 260, 270 and the drive mechanisms 280, 290 to be T₁ and T₂,respectively, it is possible to control the drive mechanisms with thegreatest level of efficiency when the conditions in equation (2) aboveare satisfied.

FIG. 17-FIG. 24 show a micro-mirror element X3 according to a thirdembodiment of the present invention. FIG. 17 is a plan view of themicro-mirror element X3, and FIG. 18 to FIG. 20 are cross-sectionalviews along line XVIII-XVIII in FIG. 17. Furthermore, FIG. 21 to FIG. 24are cross-sectional views along line XXI-XXI, line XXII-XXII, lineXXIII-XXIII, line XXIV-XXIV and line XV-XV in FIG. 17, respectively.

The micro-mirror element X3 comprises a mirror section 310, a frame 320,a pair of connecting sections 330, and respective pairs of drivemechanisms 340, 350, 360, 370. Moreover, similarly to the micro-mirrorelement X1, the micro-mirror element X3 is manufactured by carrying outprocessing on a material substrate, which is an SOI substrate having aprescribed laminated structure, by means of a bulk micro-machiningtechnology, such as MEMS technology, or the like. The material substratehas a laminated structure consisting, for example, of first and secondsilicon layers, and an insulating layer interposed between these siliconlayers, a prescribed type of conductivity being imparted to therespective silicon layers by doping with an impurity. For the purpose ofclarifying the diagrams, in FIG. 17, the areas originating in the firstsilicon layer which project in the direction of the reader beyond theinsulating layer are marked by diagonal hatching (with the exception ofthe mirror surface 311).

The mirror section 310 is a region formed principally in the firstsilicon layer, and it has a mirror surface 311 having a light reflectingfunction, on the front surface thereof. The mirror surface 311 has alaminated structure consisting of a Cr layer formed on the first siliconlayer, and an Ar layer formed on the Cr layer. The mirror surface 310 ofthis kind forms the movable section of the present invention. The frame320 is a region formed principally in the first silicon layer, in such astate that it surrounds the mirror section 310.

The pair of connecting sections 330 are regions formed in the firstsilicon layer, and consist respectively of two torsion bars 331. Therespective torsion bars 331 are connected to the mirror section 310 andthe frame 320, thus linking same together. The interval between the twotorsion bars 330 of the respective connecting sections 331 graduallyincreases from the frame 320 side towards the mirror section 310 side.The pair of connecting sections 330 of this kind define an axis A3 forthe rotational operation of the mirror section 310 with respect to theframe 320. Preferably, the connecting sections 330 which are constitutedby two torsion bars 331, the interval between which gradually increasesfrom the frame 320 side towards the mirror section 310 side, preventunwanted displacement in the rotational operation of the mirror section310. Furthermore, it is also possible to constitute the connectingsections 330 such that two different electric potentials can be appliedfrom the frame 320 to the mirror section 310, via the two torsion bars331.

Two drive mechanisms 340 are disposed in a symmetrical fashion, withrespect to the mirror section 310, each comprising a comb tooth-shapedelectrode 341 and comb tooth-shaped electrode 345. The comb tooth-shapedelectrode 341 is a region originating principally in the first siliconlayer, and it has a base section 342 which is fixed to the mirrorsection 310, and a plurality of electrode teeth 343 which project fromthis base section 342. The comb tooth-shaped electrode 345 is a regionoriginating principally in the second silicon layer, and it has a basesection 346 which is fixed to the frame 320 and projects in an inwarddirection, and a plurality of electrode teeth 347 which project fromthis base section 346. When the element is not driven in rotation, thecomb tooth-shaped electrodes 341, 345 are positioned at mutuallydifferent heights, as illustrated by FIG. 18 and FIG. 21A. Moreover, thecomb tooth-shaped electrodes 341, 345 are disposed in a state wherebytheir respective electrode teeth 343, 347 lie in mutually displacedpositions, such that they do not make contact with each other when theelement is driven in rotation.

Two drive mechanisms 350 are disposed in a symmetrical fashion, withrespect to the mirror section 310, each comprising a comb tooth-shapedelectrode 351 and comb tooth-shaped electrode 355. The comb tooth-shapedelectrode 351 is a region originating principally in the first siliconlayer, and it has a base section 352 which is fixed to the mirrorsection 310, and a plurality of electrode teeth 353 which project fromthis base section 352. The comb tooth-shaped electrode 355 is a regionoriginating principally in the second silicon layer, and it has a basesection 356 which is fixed to the frame 320 and projects in an inwarddirection, and a plurality of electrode teeth 357 which project fromthis base section 356. When the element is not driven in rotation, thecomb tooth-shaped electrodes 351, 355 are positioned at mutuallydifferent heights, as illustrated by FIG. 18 and FIG. 22A. Moreover, thecomb tooth-shaped electrodes 351, 355 are disposed in a state wherebytheir respective electrode teeth 353, 357 lie in mutually displacedpositions, such that they do not make contact with each other when theelement is driven in rotation.

Two drive mechanisms 360 are disposed in a symmetrical fashion, withrespect to the mirror section 310, each comprising a comb tooth-shapedelectrode, 361 and comb tooth-shaped electrode 365. The combtooth-shaped electrode 361 is a region originating principally in thefirst silicon layer, and it has a base section 362 which is fixed to themirror section 310, and a plurality of electrode teeth 363 which projectfrom this base section 362. The comb tooth-shaped electrode 365 is aregion originating principally in the second silicon layer, and it has abase section 366 which is fixed to the frame 320 and projects in aninward direction, and a plurality of electrode teeth 367 which projectfrom this base section 366. When the element is not driven in rotation,the comb tooth-shaped electrodes 361, 365 are positioned at mutuallydifferent heights, as illustrated by FIG. 18 and FIG. 23A. Moreover, thecomb tooth-shaped electrodes 361, 365 are disposed in a state wherebytheir respective electrode teeth 363, 367 lie in mutually displacedpositions, such that they do not make contact with each other when theelement is driven in rotation.

Two drive mechanisms 370 are disposed in a symmetrical fashion, withrespect to the mirror section 310, each comprising a comb tooth-shapedelectrode 371 and comb tooth-shaped electrode 375. The comb tooth-shapedelectrode 371 is a region originating principally in the first siliconlayer, and it has a base section 372 which is fixed to the mirrorsection 310, and a plurality of electrode teeth 373 which project fromthis base section 372. The comb tooth-shaped electrode 375 is a regionoriginating principally in the second silicon layer, and it has a basesection 376 which is fixed to the frame 320 and projects in an inwarddirection, and a plurality of electrode teeth 377 which project fromthis base section 376. When the element is not driven in rotation, thecomb tooth-shaped electrodes 371, 375 are positioned at mutuallydifferent heights, as illustrated by FIG. 18 and FIG. 24A. Moreover, thecomb tooth-shaped electrodes 371, 375 are disposed in a state wherebytheir respective electrode teeth 373, 377 lie in mutually displacedpositions, such that they do not make contact with each other when theelement is driven in rotation.

In the micro-mirror element X3, by applying prescribed electricpotentials, as and when necessary, to the respective comb tooth-shapedelectrodes 341, 345, 351, 355, 361, 365, 371, 375, it is possible tocause the mirror section 310 to rotate about the axis of rotation A3.

For example, by applying a prescribed electric potential to the combtooth-shaped electrodes 341, 345 of the drive mechanisms 340, aprescribed electrostatic attraction is generated between the combtooth-shaped electrodes 341, 345, and by applying a prescribed electricpotential to the comb tooth-shaped electrodes 361, 365 of the drivemechanisms 360, a prescribed electrostatic attraction is generatedbetween the comb tooth-shaped electrodes 361, 365, whereby the combtooth-shaped electrodes 341 are respectively drawn inside the combtooth-shaped electrodes 345, and the comb tooth-shaped electrodes 361are respectively drawn inside the comb tooth-shaped electrodes 365, suchthat the drive mechanisms 340, 360 each assume the orientationsillustrated in FIG. 19A, FIG. 21B and FIG. 23B, for example. By thismeans, the mirror section 310 performs rotational operation about theaxis of rotation A3, with respect to the frame 320. The amount ofrotational displacement performed in this rotational operation can begoverned by adjusting the applied electric potential. Rotational driveof the mirror section 310 in the opposite direction about the axis ofrotation A3 can be achieved as illustrated in FIG. 20A, FIG. 22B andFIG. 24B, for example, by generating a prescribed electrostaticattraction by means of the drive mechanisms 350, 370, in a similarmanner to the operation described above with respect to the drivemechanisms 340, 360. By driving rotation of the mirror section 310 intwo directions in this fashion, it is possible to switch the directionof reflection of the light reflected by the mirror surface 311 providedon the mirror section 310, as appropriate.

FIG. 25 shows one example of a drive mode for the micro-mirror elementX3. FIG. 25A illustrates the change over time of the voltage applied tothe comb tooth-shaped electrodes 345 of the drive mechanisms 340. FIG.25B illustrates the change over time of the voltage applied to the combtooth-shaped electrodes 365 of the drive mechanisms 360. FIG. 25Cillustrates the change over time of the voltage applied to the combtooth-shaped electrodes 355 of the drive mechanisms 350. FIG. 25Dillustrates the change over time of the voltage applied to the combtooth-shaped electrodes 375 of the drive mechanisms 370. In therespective graphs in FIG. 25A-FIG. 25D, the time (t) is represented onthe horizontal axis, and the applied voltage (v) is represented on thevertical axis. In the present drive mode, the comb tooth-shapedelectrodes 341, 351, 361, 371 are connected to ground. Furthermore, FIG.25E shows the change over time of the angle of rotation of the mirrorsection 310 in the present drive mode. In the graph in FIG. 25E, time(t) is represented on the horizontal axis, and the angle of rotation (θ)is represented on the vertical axis.

In the present drive mode, firstly, between time T₀ and T₁, a prescribedvoltage V₁ is applied to the comb tooth-shaped electrodes 345 asillustrated in FIG. 25A, and between T₀ and T₂, a prescribed voltage V₂is applied to the comb tooth-shaped electrodes 365 as illustrated inFIG. 25B, such that the rotational displacement of the mirror section310, which is in an initial state (angle of rotation of 0°) at time T₀,reaches a maximum angle of rotation θ₁ at time T₂ Between time T₀ andtime T₁, an electrostatic attraction is generated between the combtooth-shaped electrodes 341, 345 and between the comb tooth-shapedelectrodes 361, 365, and the angle of rotation of the mirror section 310increases continuously in a first direction, and at time T₁, the drivemechanisms 340, 360 assume the orientation illustrated in FIG. 19A, FIG.21B and FIG. 23B, for example. At time T₁, prior to the time at whichthe rotational displacement (for example, θ₁′), which can be generatedin the drive mechanisms 340 by a driving force (driving torque) in asecond direction opposite to the first direction, is reached, thevoltage applied to the comb tooth-shaped electrodes 345 is setsubstantially to 0V. Between time T₁ and T₂, an electrostatic attractionis generated between the comb tooth-shaped electrodes 361, 365, and theangle of rotation of the mirror section 310 increases continuously in afirst direction. At time T₂, the drive mechanisms 340, 360 assume theorientation illustrated in FIG. 19B, FIG. 21C and FIG. 23C, for example,and the angle of rotation reaches θ₁, as illustrated in FIG. 25E. Inthis case, a prescribed twisting reaction is generated in the connectingsections 330.

Thereupon, at time T₂, the voltage applied to the respective combtooth-shaped electrodes 365 is set substantially to 0V. Subsequently,between time T₂ and T₃, the twisting reaction of the connecting sections330 acts as a restoring force, and the angle of rotation decreasescontinuously. At time T₃, the angle of rotation reaches 0°, asillustrated in FIG. 25E.

Thereupon, between time T₃ and time T₄, a prescribed voltage V₃ isapplied to the comb tooth-shaped electrodes 355 as illustrated in FIG.25C, and between T₃ and T₅, a prescribed voltage V₄ is applied to thecomb tooth-shaped electrodes 375 as illustrated in FIG. 25D, such thatthe rotational displacement of the mirror section 310 reaches a maximumangle of rotation θ₂ at time t₅. Between time T₃ and time T₄, anelectrostatic attraction is generated between the comb tooth-shapedelectrodes 351, 355 and between the comb tooth-shaped electrodes 371,375, and the angle of rotation of the mirror section 310 increasescontinuously in a second direction, and at time T₄, the drive mechanisms350, 370 assume the orientation illustrated in FIG. 20A, FIG. 22B andFIG. 24B4 for example. At time T₄, prior to the time at which therotational displacement (for example, θ₂′), which can be generated inthe drive mechanisms 350 by a driving force (driving torque) in a firstdirection opposite to the second direction, is reached, the voltageapplied to the comb tooth-shaped electrodes 355 is set substantially to0V. Between time T₄ and time T₅, an electrostatic attraction isgenerated between the comb tooth-shaped electrodes 371, 375, and theangle of rotation of the mirror section 310 increases continuously inthe second direction. At time T₅, the drive mechanisms 350, 370 assumethe orientation illustrated in FIG. 20B, FIG. 22C and FIG. 24C, forexample, and the angle of rotation reaches θ₂, as illustrated in FIG.25E. In this case, a prescribed twisting reaction is generated in theconnecting sections 330.

Thereupon, at time 5, the voltage applied to the respective combtooth-shaped electrodes 375 is set substantially to 0V. Subsequently,between time T₅ and T₆, the twisting reaction of the connecting sections330 acts as a restoring force, and the angle of rotation decreasescontinuously. At time T₆, the angle of rotation reaches 0°, asillustrated in FIG. 25E. The sequence of operations described above,from time T₀ time T₆, are repeated, according to requirements.

In the present drive mode, preferably, the voltage V₁ and the voltage V₃are the same, the voltage V₂ and the voltage V₄ are the same, and theabsolute value of the angle of rotation 91 is the same as the absolutevalue of the angle of rotation θ₂. Moreover, the respective periodsbetween time T₀ and time T₂, between time T₂ and time T₃, between timeT₃ and time T₅, and between time T₅ and time T₆, are preferably set tothe same length, and each constitute respectively one quarter a cycle ofthe rotational operation of the mirror section 310. In this way, it ispossible to achieve a cyclical rotational operation of the mirrorsection 310 of the micro-mirror element X3.

FIG. 26 shows a further example of a drive mode for the micro-mirrorelement X3. FIG. 26A illustrates the change over time of the voltageapplied to the comb tooth-shaped electrodes 345 of the drive mechanisms340. FIG. 26B illustrates the change over time of the voltage applied tothe comb tooth-shaped electrodes 365 of the drive mechanisms 360. FIG.26C illustrates the change over time of the voltage applied to the combtooth-shaped electrodes 355 of the drive mechanisms 350. FIG. 26Dillustrates the change over time of the voltage applied to the combtooth-shaped electrodes 375 of the drive mechanisms 370. In therespective graphs in FIG. 26A-FIG. 26D, the time (t) is represented onthe horizontal axis, and the applied voltage (v) is represented on thevertical axis. In the present drive mode, the comb tooth-shapedelectrodes 341, 351, 361, 371 are connected to ground. Furthermore, FIG.26E shows the change over time of the angle of rotation of the mirrorsection 310 in the present drive mode. In the graph in FIG. 26E, time(t) is represented on the horizontal axis, and the angle of rotation (θ)is represented on the vertical axis. The present drive mode differs fromthe drive modes described above with reference to FIG. 25 in that thereare additional periods in which a voltage is applied to the combtooth-shaped electrodes 345, 355.

In the present drive mode, a prescribed voltage V₅ is applied to thecomb tooth-shaped electrodes 345 between time T₂ and time T₂′, asillustrated in FIG. 26A. During this period, the twisting forces of theconnecting sections 330 act as restoring forces, in addition to which anelectrostatic attraction is generated between the comb tooth-shapedelectrodes 341, 345, as a driving force in the second direction, and theangle of rotation of the mirror section 310 decreases continuously. Attime T₂′, the drive mechanisms 340, 360 assume the orientation shown inFIG. 19A, FIG. 21B and FIG. 23B, for example. At time T₂′, prior to thetime at which the rotational displacement (for example, θ₁′), which canbe generated in the drive mechanisms 340 by a driving force (drivingtorque) in a first direction opposite to the second direction, isreached, the voltage applied to the comb tooth-shaped electrodes 345 isset substantially to 0V.

Furthermore, in the present drive mode, a prescribed voltage V₆ isapplied to the comb tooth-shaped electrodes 355 between time T₅ and timeT₅′, as illustrated in FIG. 26C. During this period, the twisting forcesof the connecting sections 330 act as restoring forces, in addition towhich an electrostatic attraction is generated between the combtooth-shaped electrodes 351, 355, as a driving force in the firstdirection, and the angle of rotation of the mirror section 310 decreasescontinuously. At time T₅′, the drive mechanisms 350, 370 assume theorientation shown in FIG. 20B, FIG. 22B and FIG. 24B, for example. Attime T₅′, prior to the time at which the rotational displacement (forexample, θ₂′), which can be generated in the drive mechanisms 350 by adriving force (driving torque) in a second direction opposite to thefirst direction, is reached, the voltage applied to the combtooth-shaped electrodes 355 is set substantially to 0V.

In the present drive mode, preferably, the voltage V₁ and voltage V₅ arethe same and the voltage V₃ and voltage V₆ are the same. Moreover,preferably the sum of the respective periods between time T₀ and timeT₁, and between time T₂ and time T₂′, and the sum of the respectiveperiods between time T₃ and time T₄, and between time T₅ and time T₅′,each constitute respectively one quarter of a cycle of the rotationaloperation of the mirror section 310. In this way, it is possible toachieve a cyclical rotational operation of the mirror section 310 of themicro-mirror element X3.

In the micro-mirror element X3, the drive mechanisms 340, 350 aredisposed in mutually distant positions, and the drive mechanisms 360,370 are disposed in mutually close positions, with respect to the axisof rotation A3 of the rotational operation of the mirror section 310. Ina composition of this kind, the drive mechanisms 340, 350 are moresuitable than the drive mechanisms 360, 370, when generating a largerotational torque. For example, if the dimensional designs of the drivemechanisms 340, 350 and the drive mechanisms 360, 370 are equal, thenwhen the same voltage is applied to these drive mechanisms, a greaterrotational torque will be generated in the drive mechanisms 340, 350,compared to the drive mechanisms 360, 370, because the drive mechanisms340, 350 are situated at a greater distance from the axis of rotationA3. Moreover, the drive mechanisms 360, 370 are more suitable than thedrive mechanisms 340, 350, when a large stroke is to be ensured. Forexample, if the dimensional designs of the drive mechanisms 340, 350 andthe drive mechanisms 360, 370 are equal, then the drive mechanisms 360,370 have a stroke covering a larger amount of rotational displacement(angle of rotation) than the drive mechanisms 340, 350. In anmicro-mirror element X3 equipped with both drive mechanisms 340, 350that are suitable for generating a large rotational torque and drivemechanisms 360, 370 that are suitable for ensuring a large stroke, it ispossible to ensure an effectively large stroke even without forming therespective comb tooth-shaped electrodes of the respective drivemechanisms to an excessively thick size. In this way, the micro-mirrorelement X3 is suitable for achieving a high speed of operation forrotational operations of the mirror section 310 involving large amountsof rotational displacement.

In a micro-mirror element X3 of this kind, preferably, the drivemechanisms 340, 350 and the drive mechanisms 360, 370 are electricallyseparated and are controlled respectively in an independent fashion,such that the respective characteristics of the drive mechanisms 340,350 and the drive mechanisms 360, 370 can be utilized effectively. Forexample, in the range where the amount of displacement of the mirrorsection 310 is a small angle, a large rotational torque can be generatedby means of the drive mechanisms 340, 350, and in the range where it isa large angle, a prescribed rotational torque can be sustained in acontinuous manner, by means of the drive mechanisms 360, 370, throughoutthe relatively long stroke of these drive mechanisms 360, 370.

Moreover, in the micro-mirror element X3, by enlarging the electricfield-generating surface area of the respective comb tooth-shapedelectrodes of the drive mechanisms 360, 370 to a prescribed surfacearea, it is possible to achieve a small differential between therotational torque generated by the drive mechanisms 360, 370 and therotational torque generated by the drive mechanisms 340, 350.Alternatively, it is also possible to append a plurality of types ofdrive mechanisms for generating driving forces at yet more distantlocations from the axis of rotation A3. By adopting these compositions,it may be possible to enhance prescribed characteristics of themicro-mirror element X3.

In addition, in the micro-mirror element X3, preferably, means fordetecting the amount of rotational displacement of the mirror section310 (angle of rotation) should be provided, such that the mirror section310 can be driven in rotation with a high degree of accuracy. For suchdetecting means, it is possible to employ, for example, optical meansutilizing reflection of light at the upper face or lower face of themirror section 310, means for measuring the value of electrostaticcapacitance of the comb tooth-shaped electrodes or on the lower face ofthe mirror section 310, or means for measuring the distortion of theconnecting sections 330 or the torsion bars 331, by means of apiezo-resistance distortion gauge, or the like.

FIG. 27-FIG. 34 show a micro-mirror element X4 according to a fourthembodiment of the present invention. FIG. 27 is a plan view of themicro-mirror element X4, and FIG. 28 to FIG. 30 are cross-sectionalviews along line XXVIII-XXVIII in FIG. 27. Furthermore, FIG. 31 to FIG.34 are cross-sectional views along line XXXI-XXXI, line XXXII-XXXII,line XXXIII-XXXIII, and line XXXIV-XXXIV in FIG. 27, respectively.

The micro-mirror element X4 comprises a mirror section 310, a frame 320,a pair of connecting sections 330, and respective pairs of drivemechanisms 440, 450, 460, 470. The micro-mirror element X4 differs fromthe micro-mirror element X3 in respect of the fact that it is equippedwith drive mechanisms 440, 450, 460 and 470, instead of the drivemechanisms 340, 350, 360 and 370. Moreover, similarly to themicro-mirror element X1, the micro-mirror element X4 is manufactured bycarrying out processing on a material substrate, which is an SOIsubstrate having a prescribed laminated structure, by means of a bulkmicro-machining technology, such as MEMS technology, or the like. Thematerial substrate has a laminated structure consisting, for example, offirst and second silicon layers, and an insulating layer interposedbetween these silicon layers, a prescribed type of conductivity beingimparted to the respective silicon layers by doping with an impurity.For the purpose of clarifying the diagrams, in FIG. 27, the areasoriginating in the first silicon layer which project in the direction ofthe reader beyond the insulating layer are marked by diagonal hatching(with the exception of the mirror surface 311).

Two drive mechanisms 440 provided in the micro-mirror element X4 aredisposed in a symmetrical fashion, with respect to the mirror section310, each comprising a comb tooth-shaped electrode 441 and combtooth-shaped electrode 445. The comb tooth-shaped electrode 441 is aregion originating principally in the first silicon layer, and it has abase section 442 which is fixed to the mirror section 310, and aplurality of, electrode teeth 443 which project from this base section442. The comb tooth-shaped electrode 445 has a laminated structureconsisting of a conductor section 445 a, a conductor section 445 b, andan insulating section 445 c for electrically separating the twoconductor sections, and also has a base section 446 which is fixed tothe frame 320 and projects in an inward direction, and a plurality ofelectrode teeth 447 which project from this base section 446. Theconductor sections 445 a, 445 b are regions which originate respectivelyin the first and second silicon layers. When the element is not drivenin rotation, the comb tooth-shaped electrode 441 and the base section445 b of the comb tooth-shaped electrode 445 are positioned at mutuallydifferent heights, as illustrated by FIG. 28 and FIG. 31A. Moreover, thecomb tooth-shaped electrodes 441, 445 are disposed in a state wherebytheir respective electrode teeth 443, 447 lie in mutually displacedpositions, such that they do not make contact with each other.

Two drive mechanisms 450 are disposed in a symmetrical fashion, withrespect to the mirror section 310, each comprising a comb tooth-shapedelectrode 451 and comb tooth-shaped electrode 455. The comb tooth-shapedelectrode 451 is a region originating principally in the first siliconlayer, and it has a base section 452 which is fixed to the mirrorsection 310, and a plurality of electrode teeth 453 which project fromthis base section 452. The comb tooth-shaped electrode 455 has alaminated structure consisting of a conductor section 455 a, a conductorsection 455 b, and an insulating section 455 c for electricallyseparating the two conductor sections, and also has a base section 456which is fixed to the frame 320 and projects in an inward direction, anda plurality of electrode teeth 457 which project from this base section456. The conductor sections 455 a, 455 b are regions which originaterespectively in the first and second silicon layers. When the element isnot driven in rotation, the comb tooth-shaped electrode 451 and the basesection 455 b of the comb tooth-shaped electrode 455 are positioned atmutually different heights, as illustrated by FIG. 28 and FIG. 32A.Moreover, the comb tooth-shaped electrodes 451, 455 are disposed in astate whereby their respective electrode teeth 453, 457 lie in mutuallydisplaced positions, such that they do not make contact with each other.

Two drive mechanisms 460 are disposed in a symmetrical fashion, withrespect to the mirror section 310, each comprising a comb tooth-shapedelectrode 461 and comb tooth-shaped electrode 465. The comb tooth-shapedelectrode 461 is a region originating principally in the first siliconlayer, and it has a base section 462 which is fixed to the mirrorsection 310, and a plurality of electrode teeth 463 which project fromthis base section 462. The comb tooth-shaped electrode 465 has alaminated structure consisting of a conductor section 465 a, a conductorsection 465 b, and an insulating section 465 c for electricallyseparating the two conductor sections, and also has a base section 466which is fixed to the frame 320 and projects in an inward direction, anda plurality of electrode teeth 467 which project from this base section466. The conductor sections 465 a, 465 b are regions which originaterespectively in the first and second silicon layers. When the element isnot driven in rotation, the comb tooth-shaped electrode 461 and the basesection 465 b of the comb tooth-shaped electrode 465 are positioned atmutually different heights, as illustrated by FIG. 28 and FIG. 33A.Moreover, the comb tooth-shaped electrodes 461, 465 are disposed in astate whereby their respective electrode teeth 463, 467 lie in mutuallydisplaced positions, such that they do not make contact with each other.

Two drive mechanisms 470 are disposed in a symmetrical fashion, withrespect to the mirror section 310, each comprising a comb tooth-shapedelectrode 471 and comb tooth-shaped electrode 475. The comb tooth-shapedelectrode 471 is a region originating principally in the first siliconlayer, and it has a base section 472 which is fixed to the frame 320,and a plurality of electrode teeth 473 which project from this basesection 472. The comb tooth-shaped electrode 475 has a laminatedstructure consisting of a conductor section 475 a, a conductor section475 b, and an insulating section 475 c for electrically separating thetwo conductor sections, and also has a base section 476 which is fixedto the frame 320 and projects in an inward direction, and a plurality ofelectrode teeth 477 which project from this base section 476. Theconductor sections 475 a, 475 b are regions which originate respectivelyin the first and second silicon layers. When the element is not drivenin rotation, the comb tooth-shaped electrode 471 and the base section475 b of the comb tooth-shaped electrode 475 are positioned at mutuallydifferent heights, as illustrated by FIG. 28 and FIG. 34A. Moreover, thecomb tooth-shaped electrodes 471, 475 are disposed in a state wherebytheir respective electrode teeth 473, 477 lie in mutually displacedpositions, such that they do not make contact with each other.

In the micro-mirror element X4, by applying prescribed electricpotentials, as and when necessary, to the comb tooth-shaped electrodes441, 451, 461, 471, the conductor sections 445 a, 445 b of the combtooth-shaped electrodes 445, the conductor sections 455 a, 455 b of thecomb tooth-shaped electrodes 455, the conductor sections 465 a, 465 b ofthe comb tooth-shaped electrodes 465, and the conductors sections 475 a,475 b of the comb tooth-shaped electrodes 475, it is possible to causethe mirror section 310 to perform rotational operation about the axis ofrotation A3.

FIG. 35 shows one example of a drive configuration for the micro-mirrorelement X4. FIG. 35A illustrates the change over time of the voltageapplied to the conductor sections 445 b of the comb tooth-shapedelectrodes 445 of the drive mechanisms 440. FIG. 35B illustrates thechange over time of the voltage applied to the conductor sections 465 bof the comb tooth-shaped electrodes 465 of the drive mechanisms 460.FIG. 35C illustrates the change over time of the voltage applied to theconductor sections 455 b of the comb tooth-shaped electrodes 455 of thedrive mechanisms 450. FIG. 35D illustrates the change over time of thevoltage applied to the conductor sections 475 b of the comb tooth-shapedelectrodes 475 of the drive mechanisms 470. FIG. 35E shows the changeover time of the voltage applied to the conductor sections 445 a of thecomb tooth-shaped electrodes 445 of the drive mechanisms 440, theconductor sections 455 a of the comb tooth-shaped electrodes 455 of thedrive mechanisms 450, the conductor sections 465 a of the combtooth-shaped electrodes 465 of the drive mechanisms 460, and theconductor sections 475 a of the comb tooth-shaped electrodes 475 of thedrive mechanisms 470. In the respective graphs in FIG. 35A-FIG. 35E, thetime (t) is represented on the horizontal axis, and the applied voltage(v) is represented on the vertical axis. In the present drive mode, thecomb tooth-shaped electrodes 441, 451, 461, 471 are connected to ground.Furthermore, FIG. 35F shows the change over time of the angle ofrotation of the mirror section 310 in the present drive mode. In thegraph in FIG. 35F, time (t) is represented on the horizontal axis, andthe angle of rotation (θ) is represented on the vertical axis.

In the present drive mode, firstly, between time T₀ and T₁, a prescribedvoltage V₁ is applied to the conductor sections 445 b as illustrated inFIG. 35A, and between time T₀ and time T₂, a prescribed voltage V₂ isapplied to the conductor sections 465 b as illustrated in FIG. 35B, suchthat the rotational displacement of the mirror section 310, which is inan initial state (angle of rotation of 0°) at time T₀, reaches a maximumangle of rotation θ₁ at time T₂. Between time T₀ and time T₁, anelectrostatic attraction is generated between the comb tooth-shapedelectrodes 441 and the conductor sections 445 b, and between the combtooth-shaped electrodes 461 and the conductor sections 465 b, and theangle of rotation of the mirror section 310 increases continuously in afirst direction, and at time T₁, the drive mechanisms 440, 460 assumethe orientation illustrated in FIG. 29A, FIG. 31B and FIG. 33B, forexample. At time T₁, prior to the time at which the rotationaldisplacement (for example, θ₁′), which can be generated in the drivemechanisms 440 by a driving force (driving torque) in a second directionopposite to the first direction, is reached, the voltage applied to eachconductor section 445 b is set substantially to 0V. Between time T₁ andT₂, an electrostatic attraction is generated between the combtooth-shaped electrodes 461 and the conductor sections 465 b, and theangle of rotation of the mirror section 310 increases continuously in afirst direction. At time T₂, the drive mechanisms 440, 460 assume theorientation illustrated in FIG. 29B, FIG. 31C and FIG. 33C, for example,and the angle of rotation reaches θ₁, as illustrated in FIG. 35F. Inthis case, a prescribed twisting reaction is generated in the connectingsections 330.

Thereupon, a prescribed voltage V₃ is applied to the conductor sections445 b between time T₂ and time T₃, and a prescribed voltage V₄ isapplied to the conductor sections 445 a, 455 a, 465 a, 475 a, betweentime T₂ and time T₄, as illustrated in FIG. 35E, such that the angle ofrotation reaches 0° at time T₄. Moreover, between time T₂ and time T₄,the voltage applied to the conductor sections 465 b is set substantiallyto 0V. Between time T₂ and time T₃, in addition to the twistingreactions of the connecting sections 330 acting as restoring forces, anelectrostatic attraction is generated between the comb tooth-shapedelectrodes 441 and the comb tooth-shaped electrodes 445 (conductorsections 445 a and 445 b) as a driving force in the second direction,and furthermore, electrostatic forces of attraction are also generatedbetween the comb tooth-shaped electrodes 451 and the conductor sections455 a, between the comb tooth-shaped electrodes 461 and the conductorsections 465 a, and between the comb tooth-shaped electrodes 471 and theconductor sections 475 a, as driving forces in the second direction,whereby the angle of rotation of the mirror section 310 decreasescontinuously. At time T₃, the drive mechanisms 440, 460 assume theorientation shown in FIG. 29A, FIG. 31B and FIG. 33B, for example. Attime T₃, prior to the time at which the rotational displacement (forexample, θ₁′), which can be generated in the drive mechanisms 440 by adriving force (driving torque) in a first direction opposite to thesecond direction, is reached, the voltage applied to each conductorsection 445 b is substantially set to 0V. Thereupon, between time T₃ andtime T₄, electrostatic forces of attraction continue to be generatedbetween the comb tooth-shaped electrodes 441 and the conductor sections445 a, between the comb tooth-shaped electrodes 451 and the conductorsections 455 a, between the comb tooth-shaped electrodes 461 and theconductor sections 465 a, and between the comb tooth-shaped electrodes471 and the conductor sections 475 a, and hence the angle of rotation ofthe mirror section 310 decreases continuously. At time T₄, the angle ofrotation reaches 0°, as illustrated in FIG. 35F.

Thereupon, between time T₄ and T₅, a prescribed voltage V₅ is applied tothe conductor sections 455 b as illustrated in FIG. 35D, and betweentime T₄ and time T₆, a prescribed voltage V₆ is applied to the conductorsections 475 b as illustrated in FIG. 35D, such that the rotationaldisplacement of the mirror section 310 reaches a maximum angle ofrotation θ₂ at time T₆ Between time T₄ and time T₅, an electrostaticattraction is generated between the comb tooth-shaped electrodes 451 andthe conductor sections 455 b, and between the comb tooth-shapedelectrodes 471 and the conductor sections 475 b, and the angle ofrotation of the mirror section 310 increases continuously in a seconddirection, and at time T₅, the drive mechanisms 450, 470 assume theorientation illustrated in FIG. 30A, FIG. 32B and FIG. 34B, for example.At time T₅, prior to the time at which the rotational displacement (forexample, θ₂′), which can be generated in the drive mechanisms 450 by adriving force (driving torque) in a first direction opposite to thesecond direction, is reached, the voltage applied to each conductorsection 455 b is substantially set to 0V. Between time T₅ and T₆, anelectrostatic attraction continues to be generated between the combtooth-shaped electrodes 471 and the conductor sections 475 b, and theangle of rotation of the mirror section 310 increases continuously inthe second direction. At time T₆, the drive mechanisms 450, 470 assumethe orientation illustrated in FIG. 30B, FIG. 32C and FIG. 34C, forexample, and the angle of rotation reaches θ₂, as illustrated in FIG.35F. In this case, a prescribed twisting reaction is generated in theconnecting sections 330.

Thereupon, a prescribed voltage V₇ is applied to the conductor sections455 b between time T₆ and time T₇, as illustrated in FIG. 35C, and aprescribed voltage V₈ is applied to the conductor sections 445 a, 455 a,465 a, 475 a, between time T₆ and time T₈, as illustrated in FIG. 35E,such that the angle of rotation reaches 0° at time T₈. Moreover, betweentime T₆ and time T₈, the voltage applied to the conductor sections 475 bis set substantially to 0V. Between time T₆ and time T₇, in addition tothe twisting reactions of the connecting sections 330 acting asrestoring forces, an electrostatic attraction is generated between thecomb tooth-shaped electrodes 451 and the comb tooth-shaped electrodes455 (conductor sections 455 a and 455 b) as a driving force in the firstdirection, and furthermore, electrostatic forces of attraction are alsogenerated between the comb tooth-shaped electrodes 441 and the conductorsections 445 a, between the comb tooth-shaped electrodes 461 and theconductor sections 465 a, and between the comb tooth-shaped electrodes471 and the conductor sections 475 a, as driving forces in the firstdirection, whereby the angle of rotation of the mirror section 310decreases continuously. At time T₇, the drive mechanisms 450, 470 assumethe orientation shown in FIG. 30A, FIG. 32B and FIG. 34B, for example.At time T₇, prior to the time at which the rotational displacement (forexample, θ₂′), which can be generated in the drive mechanisms 450 by adriving force (driving torque) in a second direction opposite to thefirst direction, is reached, the voltage applied to each conductorsection 455 b is substantially set to 0V. Thereupon, between time T₇ andtime T₈, electrostatic forces of attraction continue to be generatedbetween the comb tooth-shaped electrodes 441 and the conductor sections445 a, between the comb tooth-shaped electrodes 451 and the conductorsections 455 a, between the comb tooth-shaped electrodes 461 and theconductor sections 465 a, and between the comb tooth-shaped electrodes471 and the conductor sections 475 a, and hence the angle of rotation ofthe mirror section 310 decreases continuously. At time T₈, the angle ofrotation reaches 0°, as illustrated in FIG. 35F. The sequence ofoperations described above, from time T₀ time T₈, are repeated,according to requirements.

In the present drive mode, preferably, the voltage V1 and the voltage V₃are the same, the voltage V₅ and the voltage V₇ are the same, and theabsolute value of the angle of rotation θ₁ is the same as the absolutevalue of the angle of rotation θ₂. Moreover, the respective periodsbetween time T₀ and time T₂, between time T₂ and time T₄, between timeT₄ and time T₆, and between time T₆ and time T₈, are preferably set tothe same length, and each constitute one quarter of the rotationaloperation of the mirror section 310. Moreover, preferably the sum of therespective periods between time T₀ and time T₁, and between time T₂ andtime T₃, and the sum of the respective periods between time T₄ and timeT₅, and between time T₆ and time T₇, each constitute respectively onequarter of a cycle of the rotational operation of the mirror section310. In this way, it is possible to achieve a cyclical rotationaloperation of the mirror section 310 of the micro-mirror element X4.

In the micro-mirror element X4, the drive mechanisms 440, 450 aredisposed in mutually distant positions, and the drive mechanisms 460,470 are disposed in mutually close positions, with respect to the axisof rotation A3 of the rotational operation of the mirror section 310. Inthis composition, similarly to the foregoing description relating to thedrive mechanisms 340, 350, the drive mechanisms 440, 450 are moresuitable than the drive mechanisms 460, 470, for generating a largerotational torque. Moreover, similarly to the foregoing descriptionrelating to the drive mechanisms 360, 370, the drive mechanisms 460, 470are more suitable than the drive mechanisms 440, 450, for ensuring alarge stroke. Similarly to the foregoing description relating to themicro-mirror element X3, in an micro-mirror element X4 equipped withboth drive mechanisms 440, 450 that are suitable for generating a largerotational torque and drive mechanisms 460, 470 that are suitable forensuring a large stroke, it is possible to ensure an effectively largestroke even without forming the respective comb tooth-shaped electrodesof the respective drive mechanisms to an excessively thick size. In thisway, the micro-mirror element X4 is suitable for achieving a high speedof operation for rotational operations of the mirror section 310involving large amounts of rotational displacement.

In addition, similarly to the foregoing description relating tomicro-mirror element X3, in the micro-mirror element X4, preferably,means for detecting the amount of rotational displacement of the mirrorsection 310 (angle of rotation) should be provided, such that the mirrorsection 310 can be driven in rotation with a high degree of accuracy.

FIG. 36-FIG. 40 show a micro-mirror element X5 according to a fifthembodiment of the present invention. FIG. 36 is a cross-sectional viewof the micro-mirror element X5, and FIG. 37 is a cross-sectional viewalong line XXXVII-XXXVII in FIG. 36. Furthermore, FIG. 38 to FIG. 40 arecross-sectional views along line XXXVIII-XXXVIII, line XXXIX-XXXIX, andline XXXX-XXXX in FIG. 36, respectively.

The micro-mirror element X5 comprises a mirror section 510, a frame 520,a pair of connecting sections 530, and respective pairs of drivemechanisms 540, 550. Moreover, similarly to the micro-mirror element X1,the micro-mirror element X5 is manufactured by carrying out processingon a material substrate, which is an SOI substrate having a prescribedlaminated structure, by means of a bulk micro-machining technology, suchas MEMS technology, or the like. The material substrate has a laminatedstructure consisting, for example, of first and second silicon layers,and an insulating layer interposed between these silicon layers, aprescribed type of conductivity being imparted to the respective siliconlayers by doping with an impurity. For the purpose of clarifying thediagrams, in FIG. 36, the areas originating in the first silicon layerwhich are positioned beyond the insulating layer and towards the readerare marked by diagonal hatching (with the exception of the mirrorsurface 511 described hereinafter).

The mirror section 510 is a region formed principally in the firstsilicon layer, and it has a mirror surface 511 having a light reflectingfunction, on the front surface thereof. The mirror surface 511 has alaminated structure consisting of a Cr layer formed on the first siliconlayer, and an Ar layer formed on the Cr layer. The mirror surface 510 ofthis kind forms the movable section of the present invention. The frame520 is a region formed principally in the first silicon layer, in such astate that it surrounds the mirror section 510.

The pair of connecting sections 530 are regions formed in the firstsilicon layer, and consist respectively of two torsion bars 531. Therespective torsion bars 531 are connected to the mirror section 510 andthe frame 520, thus linking same together. The interval between the twotorsion bars 530 of the respective connecting sections 531 graduallyincreases from the frame 520 side towards the mirror section 510 side.The pair of connecting sections 530 of this kind define an axis A5 forthe rotational operation of the mirror section 510 with respect to theframe 520. Preferably, the connecting sections 531 which are constitutedby two torsion bars 530, the interval between which gradually increasesfrom the frame 520 side towards the mirror section 510 side, preventunwanted displacement in the rotational operation of the mirror section510. Furthermore, it is also possible to constitute the connectingsections 530 such that two different electric potentials can be appliedfrom the frame 520 to the mirror section 510, via the two torsion bars531.

Two drive mechanisms 540 are disposed in a symmetrical fashion, withrespect to the mirror section 510, each comprising a comb tooth-shapedelectrode 541 and comb tooth-shaped electrode 545. The comb tooth-shapedelectrode 541 is a region originating principally in the first siliconlayer, and it has a base section 542 which is fixed to the mirrorsection 510, and a plurality of electrode teeth 543. The base section541 extends such that it approaches the axis of rotation A5 as itbecomes more distant from the mirror section 510. A plurality ofelectrode teeth 543 of substantially the same length extends from thisbase section 541 in a perpendicular direction to the axis of rotationA5. The comb tooth-shaped electrode 545 is a region originatingprincipally in the second silicon layer, and it has a base section 546which is fixed to the frame 520 and projects in an inward direction, anda plurality of electrode teeth 547. The base section 546 extends suchthat it becomes more distant from the axis of rotation A5 as approachingthe mirror section 510. A plurality of electrode teeth 547 ofsubstantially the same length extend from this base section 546 in aperpendicular direction to the axis of rotation A5. When the element isnot driven in rotation, the comb tooth-shaped electrodes 541 and thecomb tooth-shaped electrodes 545 are positioned at mutually differentheights, as illustrated by FIG. 37A, FIG. 38A and FIG. 39A. Moreover,the comb tooth-shaped electrodes 541, 545 are disposed in a statewhereby their respective electrode teeth 543, 547 lie in mutuallydisplaced positions, such that they do not make contact with each other.

Two drive mechanisms 550 are disposed in a symmetrical fashion, withrespect to the mirror section 510, each comprising a comb tooth-shapedelectrode 551 and comb tooth-shaped electrode 555. The comb tooth-shapedelectrode 551 is a region originating principally in the first siliconlayer, and it has a base section 552 which is fixed to the mirrorsection 510, and a plurality of electrode teeth 553. The base section551 extends such that it approaches the axis of rotation A5 as itbecomes more distant from the mirror section 510. A plurality ofelectrode teeth 553 of substantially the same length extend from thisbase section 551 in a perpendicular direction to the axis of rotationA5. The comb tooth-shaped electrode 555 is a region originatingprincipally in the second silicon layer, and it has a base section 556which is fixed to the frame 520 and projects in an inward direction, anda plurality of electrode teeth 557. The base section 556 extends suchthat it becomes more distant from the axis of rotation A5 as approachingthe mirror section 510. A plurality of electrode teeth 557 ofsubstantially the same length extend from this base section 556 in aperpendicular direction to the axis of rotation A5. When the element isnot driven in rotation, the comb tooth-shaped electrodes 551 and thecomb tooth-shaped electrodes 555 are positioned at mutually differentheights, as illustrated by FIG. 37A, FIG. 38A and FIG. 40A. Moreover,the comb tooth-shaped electrodes 551, 555 are disposed in a statewhereby their respective electrode teeth 553, 557 lie in mutuallydisplaced positions, such that they do not make contact with each other.

In the micro-mirror element X5, by applying prescribed electricpotentials, as and when necessary, to the respective comb tooth-shapedelectrodes 541, 545, 551, 555, it is possible to cause the mirrorsection 510 to rotate about the axis of rotation A5.

For example, by applying a prescribed electric potential to the combtooth-shaped electrodes 541, 545 of the drive mechanisms 540, aprescribed electrostatic attraction is generated between the combtooth-shaped electrodes 541, 545, whereby the comb tooth-shapedelectrode 541 is drawn inside the comb tooth-shaped electrode 545, suchthat the respective electrodes assume the orientation illustrated inFIG. 37B, FIG. 38B, and FIG. 39B, for example. By this means, the mirrorsection 510 performs rotational operation about the axis of rotation A5,with respect to the frame 520. The amount of rotational displacementperformed in this rotational operation can be governed by adjusting theapplied electric potential. The mirror section 510 can be driven inrotation in the opposite direction about the axis of rotation A5 bygenerating a prescribed electrostatic attraction in the drive mechanisms550, similarly to the foregoing description relating to the drivemechanisms 540. By driving rotation of the mirror section 510 in twodirections in this fashion, it is possible to switch the direction ofreflection of the light reflected by the mirror surface 511 provided onthe mirror section 510, as appropriate.

In the micro-mirror element X5, the stroke based on the most proximatelypositioned electrode teeth 543, 547 in each drive mechanism 540, and thestroke based on the most proximately positioned electrode teeth 553, 557in each drive mechanism 550, change continuously in a direction parallelto the electrode teeth. More specifically, the stroke based on the mostproximately positioned electrode teeth 543, 547, and the stroke based onthe most proximately positioned electrode teeth 553, 557 increasesgradually from the mirror section 510 side to the frame 520 side.Therefore, in the micro-mirror element X5, it is possible to ensure aneffectively long stroke, even without forming the comb tooth-shapedelectrodes 541, 545, 551, 555 of the drive mechanisms 540, 550 to anexcessively thick size. In this way, the micro-mirror element X5 issuitable for achieving a high speed of operation for rotationaloperations of the mirror section 510 involving large amounts ofrotational displacement.

Furthermore, in the micro-mirror element X5, the rotational torquegenerated between the most proximately positioned electrode teeth 543,547 in each drive mechanism 540, and the rotational torque generatedbetween the most proximately positioned electrode teeth 553, 557 in eachdrive mechanism 550, change continuously in a direction parallel to theelectrode teeth. More specifically, the rotational torque generatedbetween the most proximately positioned electrode teeth 543, 547, andthe rotational torque generated between the most proximately positionedelectrode teeth 553, 557 increases gradually from the frame 520 side tothe mirror section 510 side. Consequently, in the micro-mirror elementX5, it is possible to avoid generating sudden variations in torque overa relatively broad range of rotational operation of the mirror section510.

FIG. 41 and FIG. 42 show a modification example of comb tooth-shapedelectrodes constituting respective drive mechanisms of micro-mirrorelements X1, X3 and X5. FIG. 41A-FIG. 41D show cross-sectional views ofcomb tooth-shaped electrodes according to respective modificationexamples, and FIG. 42A and FIG. 42B are respective partial plan views ofmodification examples.

In the modification illustrated in FIG. 41A, a fixed comb tooth-shapedelectrode has electrode teeth 71 and a moving comb tooth-shapedelectrode has electrode teeth 71′. When the element is not driven, theelectrode teeth 71 and the electrode teeth 71′ overlap partially in thedirection of the thickness of the comb tooth-shaped electrodes. Here,the fixed comb tooth-shaped electrode corresponds, for example to thecomb tooth-shaped electrodes 165, 175, 185, 195 in the micro-mirrorelement X1, or to the comb tooth-shaped electrodes 345, 355, 365, 375 inthe micro-mirror element X3, or to the comb tooth-shaped electrodes 545,555 in the micro-mirror element X5. On the other hand, the movable combtooth-shaped electrode corresponds, for example to the comb tooth-shapedelectrodes 161, 171, 181, 191 in the micro-mirror element X1, or to thecomb tooth-shaped electrodes 341, 351, 361, 371 in the micro-mirrorelement X3, or to the comb tooth-shaped electrodes 541, 551 in themicro-mirror element X5. This applies similarly to the othermodification examples described below. In the present modification, theelectrode teeth 71 each have a laminated structure consisting ofconductor sections 71 a, 71 b, and an insulating section 71 c interposedbetween same. In the electrode teeth 71, the conductor sections 71 a, 71b are electrically connected. In a composition of this kind, since theelectrode teeth 71 and the electrode teeth 71′ are already partiallyoverlapping when the element is not driven in rotation, then it ispossible to reduce sudden changes in the rotational torque in the rangeof small angles of rotation on either side of 0°.

In the modification illustrated in FIG. 41B, a moving comb tooth-shapedelectrode has electrode teeth 72 and a fixed comb tooth-shaped electrodehas electrode teeth 72′. When the element is not driven, the electrodeteeth 72 and the electrode teeth 72′ overlap partially in the directionof the thickness of the comb tooth-shaped electrodes. In the presentmodification, the comb tooth-shaped electrode 72 has a laminatedstructure consisting of conductor sections 72 a, 72 b, and an insulatingsection 72 c interposed between same. In the electrode teeth 72, theconductor sections 72 a, 72 b are electrically connected. In acomposition of this kind, since the electrode teeth 72 and the electrodeteeth 72′ are already partially overlapping when the element is notdriven in rotation, then it is possible to reduce sudden changes in therotational torque in the range of small angles of rotation on eitherside of 0°.

In the modification illustrated in FIG. 41C, a fixed comb tooth-shapedelectrode has electrode teeth 73 and a moving comb tooth-shapedelectrode has electrode teeth 73′. When the element is not driven, theelectrode teeth 73 and the electrode teeth 73′ overlap partially in thedirection of the thickness of the comb tooth-shaped electrodes. Therespective electrode teeth 73, 73, are each made from a uniformconducting section. In a composition of this kind, since the electrodeteeth 73 and the electrode teeth 73′ are already partially overlappingwhen the element is not driven in rotation, then it is possible toreduce sudden changes in the rotational torque in the range of smallangles of rotation on either side of 0°.

In the modification illustrated in FIG. 41D, a fixed comb tooth-shapedelectrode has electrode teeth 74 and a moving comb tooth-shapedelectrode has electrode teeth 74′. The electrode teeth 74, which arelocated in a lower position when the element is not driven in rotation,are designed such that they gradually become wider, from the bottomtowards the top thereof, whereas the electrode teeth 74′ which arelocated in an upper position when the element is not driven in rotation,are designed such that they gradually become wider from the top towardsthe bottom thereof. According to a composition of this kind, by reducingsudden changes in rotational torque in the range of small angles ofrotation either side of 0°, and reducing the rotational torque in thecase of large angles, it is possible to reduce variation in capacitanceafter the comb tooth-shaped electrode has been withdrawn (afterdeparture of the stroke). Moreover, according to this composition, it isalso possible to increase the bending strength of the respectiveelectrode teeth.

In the modification in FIG. 42A, the outermost electrode tooth 75 is setto a thicker dimension than the other electrode teeth. When a voltage isapplied, the outermost electrode tooth in a drive mechanism constitutedby a set of comb tooth-shaped electrodes receives a large electrostaticbending force acting in the inward direction of the drive mechanism, butby means of the present composition, it is possible to prevent theoutermost electrode tooth 75 from bending excessively, due to thiselectrostatic force.

In the modification shown in FIG. 42B, respective electrode teeth 77extending from a base section 76 are designed such that they becomegradually wider from the free end towards the base end thereof. By meansof a composition of this kind, it is possible to improve the bendingstrength of the electrode teeth 77, suitably.

1-19. (canceled)
 20. A method for driving a micro-oscillation element,the element comprising: a movable section, a frame, a connecting sectionthat connects the movable section and the frame and defines an axis ofrotation for the rotational operation of the movable section withrespect to the frame, a first comb tooth-shaped electrode and a secondcomb tooth-shaped electrode for generating a driving force forrotational operation, and a third comb tooth-shaped electrode and afourth comb tooth-shaped electrode for generating a driving force forrotational operation at a position closer to the axis of rotation thanthe first and second comb tooth-shaped electrodes; wherein the drivingmethod comprises: a first step for causing the movable section toperform rotational operation in a first direction by generating anelectrostatic attraction between the first comb tooth-shaped electrodeand the second comb tooth-shaped electrode, as well as generating anelectrostatic attraction between the third comb tooth-shaped electrodeand the fourth comb tooth-shaped electrode; and a second step forcausing the movable section to perform rotational operation in a firstdirection by generating an electrostatic attraction, following the firststep, between the third comb tooth-shaped electrode and the fourth combtooth-shaped electrode.
 21. The method for driving a micro-oscillationelement according to claim 20, further comprising a third step, forcausing the movable section to perform rotational operation in a seconddirection, opposite to the first direction, by generating anelectrostatic attraction between the first conductor section and thesecond conductor section, subsequently to the second step.
 22. Themethod for driving a micro-oscillation element according to claim 21,wherein the first step and third step are both implemented during a timeperiod corresponding to one quarter of a cycle of the rotationaloperation.
 23. The method for driving a micro-oscillation elementaccording to claim 20, wherein the micro-oscillation element furthercomprises a fifth comb tooth-shaped electrode and a sixth combtooth-shaped electrode for generating a driving force for rotationaloperation, and a seventh comb tooth-shaped electrode and eighth combtooth-shaped electrode for generating a driving force for rotationaloperation at a position closer to the axis of rotation than the fifthand sixth comb tooth-shaped electrodes; wherein the driving methodfurther comprises: a fourth step for causing the movable section toperform rotational operation in a second direction by generating anelectrostatic attraction between the fifth comb tooth-shaped electrodeand the sixth comb tooth-shaped electrode, as well as generating anelectrostatic attraction between the seventh comb tooth-shaped electrodeand the eighth comb tooth-shaped electrode, subsequently to the thirdstep; and a fifth step for causing the movable section to performrotational operation in a second direction by generating anelectrostatic attraction, following the fourth step, between the seventhcomb tooth-shaped electrode and the eighth comb tooth-shaped electrode.24. The method for driving a micro-oscillation element according toclaim 23, further comprising a sixth step for causing the movablesection to perform rotational operation in the first direction bygenerating an electrostatic attraction between the fifth combtooth-shaped electrode and the sixth comb tooth-shaped electrode,subsequently to the fifth step.
 25. The method for driving amicro-oscillation element according to claim 24, wherein the fifth stepand sixth step are both implemented during a time period correspondingto one quarter of a cycle of the rotational operation.
 26. A method fordriving a micro-oscillation element, the element comprising: a movablesection, a frame, a connecting section that connects the movable sectionand the frame and defines an axis of rotation for the rotationaloperation of the movable section with respect to the frame, a first combtooth-shaped electrode and a second comb tooth-shaped electrode forgenerating a driving force for rotational operation, and a third combtooth-shaped electrode and a fourth comb tooth-shaped electrode forgenerating a driving force for rotational operation at a position closerto the axis of rotation than the first and second comb tooth-shapedelectrodes; the first comb tooth-shaped electrode having electrode teethcomprising a first conductor section and a second conductor sectionaligned in parallel with the direction of rotational operation; thesecond comb tooth-shaped electrode having electrode teeth comprising athird conductor section that opposes the first conductor section anddoes not oppose the second conductor section when the element is notdriven; the third comb tooth-shaped electrode having electrode teethcomprising a fourth conductor section and a fifth conductor sectionaligned in parallel with the direction of rotational operation; and thefourth comb tooth-shaped electrode having electrode teeth comprising asixth conductor section that opposes the fourth conductor section anddoes not oppose the fifth conductor section when the element is notdriven; wherein the driving method comprises: a first step for causingthe movable section to perform rotational operation in a first directionby generating an electrostatic attraction between the second conductorsection and the third conductor section, as well as generating anelectrostatic attraction between the fifth conductor section and thesixth conductor section; and a second step for causing the movablesection to perform rotational operation in a first direction bygenerating an electrostatic attraction, following the first step,between the fifth conductor section and the sixth conductor section. 27.The method for driving a micro-oscillation element according to claim26, further comprising: a third step for causing the movable section toperform rotational operation in a second direction, opposite to thefirst direction, by generating an electrostatic attraction between thefirst conductor section and the third conductor section, between thesecond conductor section and the third conductor section, and betweenthe fourth conductor section and the sixth conductor section,subsequently to the second step; and a fourth step for causing themovable section to perform rotational operation in the second directionby generating an electrostatic attraction, following the third step,between the first conductor section and the third conductor section, andbetween the fourth conductor section and the sixth conductor section.28. The method for driving a micro-oscillation element according toclaim 27, wherein the micro-oscillation element further comprises afifth comb tooth-shaped electrode and a sixth comb tooth-shapedelectrode for generating a driving force for rotational operation, and aseventh comb tooth-shaped electrode and eighth comb tooth-shapedelectrode for generating a driving force for rotational operation at aposition closer to the axis of rotation than the fifth and sixth combtooth-shaped electrodes; the fifth comb tooth-shaped electrode havingelectrode teeth comprising a seventh conductor section and an eighthconductor section aligned in parallel with the direction of rotationaloperation; the sixth comb tooth-shaped electrode having electrode teethcomprising a ninth conductor section that opposes the seventh conductorsection and does not oppose the eighth conductor section when theelement is not driven; the seventh comb tooth-shaped electrode havingelectrode teeth comprising a tenth conductor section and an eleventhconductor section aligned in parallel with the direction of rotationaloperation; and the eighth comb tooth-shaped electrode having electrodeteeth comprising a twelfth conductor section that opposes the tenthconductor section and does not oppose the eleventh conductor sectionwhen the element is not driven; wherein the driving method furthercomprises: a fifth step for causing the movable section to performrotational operation in a second direction by generating anelectrostatic attraction between the eighth conductor section and theninth conductor section, as well as generating an electrostaticattraction between the eleventh conductor section and the twelfthconductor section, subsequently to the fourth step; a sixth step forcausing the movable section to perform rotational operation in a seconddirection by generating an electrostatic attraction, following the fifthstep, between the eleventh conductor section and the twelfth conductorsection; a seventh step for causing the movable section to performrotational operation in a first direction by generating an electrostaticattraction between the seventh conductor section and the ninth conductorsection, between the eighth conductor section and the ninth conductorsection, and between the tenth conductor section and the twelfthconductor section, subsequently to the sixth step; and an eighth stepfor causing the movable section to perform rotational operation in thefirst direction by generating an electrostatic attraction, following theseventh step, between the seventh conductor section and the ninthconductor section, and between the tenth conductor section and thetwelfth conductor section.
 29. The method for driving amicro-oscillation element according to claim 28, wherein, in the thirdstep and the fourth step, an electrostatic attraction is generatedbetween the seventh conductor section and the ninth conductor section,and between the tenth conductor section and the twelfth conductorsection.
 30. The method for driving a micro-oscillation elementaccording to claim 28, wherein, in the seventh step and the eighth step,an electrostatic attraction is generated between the first conductorsection and the third conductor section, and between the fourthconductor section and the sixth conductor section.